Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Share-based compensation expense Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block] Supplemental Financial Information [Abstract] Supplemental Financial Information [Abstract] Property, Plant and Equipment [Table] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Domain] Property, Plant and Equipment, Type [Domain] Leasehold Improvements [Member] Leasehold Improvements [Member] Furniture, Fixtures, and Equipment [Member] Furniture, Fixtures, and Equipment [Member] Furniture, Fixtures, and Equipment [Member] Construction in Progress [Member] Construction in Progress [Member] Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Property and equipment, gross Property, Plant and Equipment, Gross Accumulated depreciation and amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Property and equipment, net Property, Plant and Equipment, Net Earnings Per Share [Abstract] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Lender Name [Axis] Lender Name [Axis] Line of Credit Facility, Lender [Domain] Line of Credit Facility, Lender [Domain] L Catterton L Catterton [Member] L Catterton [Member] Antidilutive Securities [Axis] Antidilutive Securities [Axis] Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Preferred Stock Preferred Stock [Member] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Document Period End Date Document Period End Date Net Income (Loss) Available to Common Stockholders, Basic Net Income (Loss) Available to Common Stockholders, Basic Net loss Net Income (Loss) Attributable to Parent Shares: Weighted Average Number of Shares Outstanding Reconciliation [Abstract] Basic weighted average shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Basic Effect of dilutive securities (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Diluted weighted average number of shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Diluted Loss per share: Earnings Per Share, Basic and Diluted [Abstract] Basic loss per share (USD per share) Earnings Per Share, Basic Diluted loss per share (USD per share) Earnings Per Share, Diluted Preferred stock, shares issued (in shares) Preferred Stock, Shares Issued Antidilutive securities excluded from computation of earnings per share Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Statement of Financial Position [Abstract] Assets Assets [Abstract] Current assets: Assets, Current [Abstract] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Accounts receivable Accounts Receivable, Net, Current Inventories Inventory, Net Prepaid expenses and other assets Prepaid Expense and Other Assets, Current Income tax receivable Income Taxes Receivable, Current Total current assets Assets, Current Property and equipment, net Goodwill Goodwill Intangibles, net Intangible Assets, Net (Excluding Goodwill) Other assets, net Other Assets, Noncurrent Total long-term assets Assets, Noncurrent Total assets Assets Liabilities and Stockholders’ Equity Liabilities and Equity [Abstract] Current liabilities: Liabilities, Current [Abstract] Accounts payable Accounts Payable, Current Accrued payroll and benefits Employee-related Liabilities, Current Accrued expenses and other current liabilities Accrued Liabilities, Current Total current liabilities Liabilities, Current Long-term debt, net Long-term Debt, Excluding Current Maturities Deferred rent Deferred Rent Credit, Noncurrent Deferred tax liabilities, net Deferred Tax Liabilities, Net Other long-term liabilities Other Liabilities, Noncurrent Total liabilities Liabilities Stockholders’ equity: Stockholders' Equity Attributable to Parent [Abstract] Preferred stock—$0.01 par value, 1,000,000 shares authorized and undesignated as of April 3, 2018 and January 2, 2018; no shares issued or outstanding Preferred Stock, Value, Issued Common stock—$0.01 par value, 180,000,000 shares authorized as of April 3, 2018 and January 2, 2018; 43,559,312 issued and 41,135,441 outstanding as of April 3, 2018 and 43,550,329 issued and 41,126,458 outstanding as of January 2, 2018 Common Stock, Value, Issued Treasury stock, at cost, 2,423,871 shares as of April 3, 2018 and January 2, 2018 Treasury Stock, Value Additional paid-in capital Additional Paid in Capital Accumulated deficit Retained Earnings (Accumulated Deficit) Total stockholders’ equity Stockholders' Equity Attributable to Parent Total liabilities and stockholders’ equity Liabilities and Equity Organization, Consolidation and Presentation of Financial Statements [Abstract] Business and Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Fiscal year Fiscal Period, Policy [Policy Text Block] Reclassification Reclassification, Policy [Policy Text Block] Recent Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Equity [Abstract] Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Class of Warrant or Right [Axis] Class of Warrant or Right [Axis] Class of Warrant or Right [Domain] Class of Warrant or Right [Domain] Common Stock Common Stock [Member] Warrant Warrant [Member] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Fair Value, Inputs, Level 2 Fair Value, Inputs, Level 2 [Member] Mill Road Capital II, L.P. Mill Road Capital II, L.P. [Member] Mill Road Capital II, L.P. [Member] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] Common Class A Common Class A [Member] Class of Stock [Line Items] Class of Stock [Line Items] Convertible preferred stock, shares issued upon conversion (in shares) Convertible Preferred Stock, Shares Issued upon Conversion Common stock, par value (USD per share) Common Stock, Par or Stated Value Per Share Price per share (in dollars per share) Sale of Stock, Price Per Share Number of securities called by each warrant or right (in shares) Class of Warrant or Right, Number of Securities Called by Each Warrant or Right Exercise price of warrants or rights (in USD per share) Class of Warrant or Right, Exercise Price of Warrants or Rights Net proceeds from issuance of private placement Proceeds from Issuance of Private Placement, Net Proceeds from Issuance of Private Placement, Net Proceeds from issuance of private placement Proceeds from Issuance of Private Placement Transaction expenses Payments for Repurchase of Private Placement Fair value of warrants Fair Value Adjustment of Warrants Embedded beneficiary conversion Debt Instrument, Convertible, Beneficial Conversion Feature Discount on convertible preferred stock Temporary Equity, Accretion of Dividends Common stock, shares, issued (in shares) Sale of Stock, Number of Shares Issued in Transaction Additional transaction expenses Payments for Repurchase of Private Placement, Additional Payments for Repurchase of Private Placement, Additional Supplemental Cash Flow Elements [Abstract] Interest paid (net of amounts capitalized) Interest Paid, Net Income taxes paid (refunded) Income Taxes Paid (Refunded) Income Taxes Paid (Refunded) Changes in purchases of property and equipment accrued in accounts payable, net Change In Capital Expenditures Incurred But Not Yet Paid Change In Capital Expenditures Incurred But Not Yet Paid Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Income Tax Disclosure [Abstract] Income Taxes Income Tax Disclosure [Text Block] Schedule of Provision for Income Taxes Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] Property, Plant and Equipment Impairment or Disposal [Abstract] Restaurant Impairment, Closure Costs and Asset Disposals Disposal Groups, Including Discontinued Operations, Disclosure [Text Block] Gift card liability Gift Card Liability, Current Occupancy related Accrued Occupancy Liability, Current Accrued Occupancy Liability, Current Utilities Accrued Utilities, Current Data breach liabilities Data Breach Liabilities Data Breach Liabilities Other accrued expenses Other Accrued Liabilities, Current Accrued liabilities, current Loss Contingencies [Table] Loss Contingencies [Table] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum [Member] Minimum [Member] Maximum [Member] Maximum [Member] Loss Contingencies [Line Items] Loss Contingencies [Line Items] Estimate of possible loss Loss Contingency, Estimate of Possible Loss Supplemental Disclosures to Condensed Consolidated Statements of Cash Flows Cash Flow, Supplemental Disclosures [Text Block] Debt Disclosure [Abstract] Long-Term Debt Debt Disclosure [Text Block] Schedule of Property and Equipment Property, Plant and Equipment [Table Text Block] Schedule of Accrued Expenses and Other Current Liabilities Schedule of Accounts Payable and Accrued Liabilities [Table Text Block] Revenue from Contract with Customer [Abstract] Revenue Recognition Revenue from Contract with Customer [Text Block] Restaurant impairments Impairment of Long-Lived Assets Held-for-use Closure costs Costs Related to Closure of Restaurants Costs Related to Closure of Restaurants Loss on disposal of assets and other Gain (Loss) on Disposition of Property Plant Equipment Asset Disposals, Closure Costs and Restaurant Impairments Asset Disposals, Closure Costs and Restaurant Impairments The gains and losses included in earnings resulting from the sale or disposal of tangible assets, asset impairment charges resulting from the write down of assets from their carrying value to their fair value, and costs incurred associated with an exit or disposal activity other than for a discontinued operations. Costs of such activities include those for one-time termination benefits, termination of an operating lease or other contract, but excludes costs associated with the retirement of a long-lived asset. Number of restaurants impaired during the comparable periods Number of Restaurants Impaired During the Comparable Periods Number of Restaurants Impaired During the Comparable Periods Number of restaurants closed Number Of Restaurants Closed Number Of Restaurants Closed Impairment closure costs and other Impairment Closure Costs And Other Impairment Closure Costs And Other Revenue, Initial Application Period Cumulative Effect Transition [Table] Revenue, Initial Application Period Cumulative Effect Transition [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Initial Application Period Cumulative Effect Transition [Line Items] Revenue, Initial Application Period Cumulative Effect Transition [Line Items] Performance obligation, period Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Performance obligation Revenue, Remaining Performance Obligation Statement of Cash Flows [Abstract] Operating activities Net Cash Provided by (Used in) Operating Activities [Abstract] Adjustments to reconcile net loss to net cash used in operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation and amortization Depreciation, Depletion and Amortization Deferred income taxes Deferred Income Tax Expense (Benefit) Restaurant impairments, closure costs and asset disposals Noncash or Part Noncash Asset Disposals, Closure Costs And Restaurant Impairments Noncash or Part Noncash Asset Disposals, Closure Costs And Restaurant Impairments Amortization of debt issuance costs Amortization of Debt Issuance Costs Stock-based compensation Share-based Compensation Changes in operating assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Accounts receivable Increase (Decrease) in Accounts Receivable Inventories Increase (Decrease) in Inventories Prepaid expenses and other assets Increase (Decrease) in Prepaid Expense and Other Assets Accounts payable Increase (Decrease) in Accounts Payable Deferred rent Increase (Decrease) In Deferred Rent Increase (Decrease) In Deferred Rent Income taxes Increase (Decrease) in Income Taxes Payable Accrued expenses and other liabilities Increase (Decrease) in Accrued Liabilities and Other Liabilities Increase (Decrease) in Accrued Liabilities and Other Liabilities Net cash used in operating activities Net Cash Provided by (Used in) Operating Activities Investing activities Net Cash Provided by (Used in) Investing Activities [Abstract] Purchases of property and equipment Payments to Acquire Property, Plant, and Equipment Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Financing activities Net Cash Provided by (Used in) Financing Activities [Abstract] Net borrowings from swing line loan Proceeds from (Repayments of) Notes Payable Proceeds from issuance of long-term debt Proceeds from Issuance of Long-term Debt Payments on long-term debt Repayments of Notes Payable Issuance of preferred stock and common stock warrants, net of transaction expenses (see Note 9) Proceeds from Issuance or Sale of Equity Issuance of common stock, net of transaction expenses (see Note 9) Proceeds from Issuance of Common Stock Proceeds from exercise of stock options and employee stock purchase plan Proceeds from Stock Options Exercised Debt issuance costs Proceeds from (Payments for) Other Financing Activities Net cash provided by financing activities Net Cash Provided by (Used in) Financing Activities Net (decrease) increase in cash and cash equivalents Cash and Cash Equivalents, Period Increase (Decrease) Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value [Abstract] Beginning of period End of period Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table] Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table] Award Type [Axis] Award Type [Axis] Equity Award [Domain] Equity Award [Domain] Employee Stock Option [Member] Employee Stock Option [Member] Subsidiary, Sale of Stock [Axis] Sale of Stock [Axis] Sale of Stock, Name of Transaction [Domain] Sale of Stock [Domain] IPO [Member] IPO [Member] Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] Maximum shares reserved for issuance Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Allocated Share-based Compensation Expense Allocated Share-based Compensation Expense Capitalized stock based compensation expense Employee Service Share-based Compensation, Allocation of Recognized Period Costs, Capitalized Amount (Benefit) provision for income taxes Income Tax Expense (Benefit) Effective tax rate Effective Income Tax Rate Reconciliation, Percent Stock-Based Compensation Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Document and Entity Information [Abstract] Document and Entity Information [Abstract] Document Information [Table] Document Information [Table] Common Class B [Member] Common Class B [Member] Document Information [Line Items] Document Information [Line Items] Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Document Type Document Type Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Amendment Flag Amendment Flag Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Schedule of Franchisor Disclosure [Table] Schedule of Franchisor Disclosure [Table] Franchisor Disclosure [Axis] Franchisor Disclosure [Axis] Franchisor Disclosure [Domain] Franchisor Disclosure [Domain] Company-Owned [Member] Entity Operated Units [Member] Franchise [Member] Franchised Units [Member] Franchisor Disclosure [Line Items] Franchisor Disclosure [Line Items] Number of restaurants Number of Restaurants Number of states with operations Number of States in which Entity Operates Number of operating segments Number of Operating Segments Number of reportable segments Number of Reportable Segments Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Initial Application Period Cumulative Effect Transition [Axis] Initial Application Period Cumulative Effect Transition [Axis] Initial Application Period Cumulative Effect Transition [Domain] Initial Application Period Cumulative Effect Transition [Domain] Calculated under Revenue Guidance in Effect on Adoption of Topic 606 Calculated under Revenue Guidance in Effect on Adoption of Topic 606 [Member] Calculated under Revenue Guidance in Effect on Adoption of Topic 606 [Member] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Accounting Standards Update 2014-09 Accounting Standards Update 2014-09 [Member] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Accrued Expenses and Other Current Liabilities Accrued Expenses and Other Current Liabilities [Member] Accrued Expenses and Other Current Liabilities [Member] Other Long-term Liabilities Other Long-term Liabilities [Member] Other Long-term Liabilities [Member] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Expected unredeemed percent Revenue Recognition, Gift Cards, Expected Unredeemed Percent Revenue Recognition, Gift Cards, Expected Unredeemed Percent Estimated redemption period Revenue Recognition, Gift Cards, Estimated Redemption Period Revenue Recognition, Gift Cards, Estimated Redemption Period Gift card liability, non-current Gift Card Liability, Non-Current Gift Card Liability, Non-Current Revenue recognized Contract with Customer, Liability, Revenue Recognized Period in which initial fees received from franchisees will be recognized as revenue Contract With Customer Period in Which Initial Fees Received from Franchisees will be Recognized as Revenue Contract With Customer Period in Which Initial Fees Received from Franchisees will be Recognized as Revenue Retained earnings Supplemental Disclosures to the Consolidated Statements of Cash Flows Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Supplemental Financial Information Supplemental Balance Sheet Disclosures [Text Block] Line of Credit Facility [Table] Line of Credit Facility [Table] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event Subsequent Event [Member] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] 2018 Credit Facility Two Thousand and Eighteen Credit Facility [Member] Two Thousand and Eighteen Credit Facility [Member] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Revolving Credit Facility Revolving Credit Facility [Member] Letter of Credit Letter of Credit [Member] Credit Subfacility Credit Subfacility [Member] Credit Subfacility [Member] Swingline Subfacility Swingline Subfacility [Member] Swingline Subfacility [Member] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] LIBOR London Interbank Offered Rate (LIBOR) [Member] Base Rate Base Rate [Member] Federal Funds Rate Federal Funds Rate [Member] Federal Funds Rate [Member] Prime Rate Prime Rate [Member] Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Amount outstanding Long-term Line of Credit Letters of credit outstanding Letters of Credit Outstanding, Amount Basis spread on variable rate Debt Instrument, Basis Spread on Variable Rate Interest rate Line of Credit Facility, Interest Rate During Period Commitment fee percentage Line of Credit Facility, Commitment Fee Percentage Schedule of Basic and Diluted Loss Per Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Loss Per Share Earnings Per Share [Text Block] Preferred stock, par value (USD per share) Preferred Stock, Par or Stated Value Per Share Preferred stock, shares authorized Preferred Stock, Shares Authorized Preferred stock, shares outstanding Preferred Stock, Shares Outstanding Common stock, shares authorized Common Stock, Shares Authorized Common stock, shares, issued (in shares) Common Stock, Shares, Issued Common stock, shares, outstanding Common Stock, Shares, Outstanding Treasury stock, shares Treasury Stock, Shares Stockholder's Equity Stockholders' Equity Note Disclosure [Text Block] Income Statement [Abstract] Revenue: Revenues [Abstract] Restaurant revenue Food and Beverage Revenue Franchising royalties and fees Franchise Revenue Total revenue Revenue, Net Costs and expenses: Costs and Expenses [Abstract] Restaurant operating costs (exclusive of depreciation and amortization shown separately below): Operating Expenses [Abstract] Cost of sales Food and Beverage, Cost of Sales Labor Cost of Goods Sold, Direct Labor Occupancy Occupancy, Net Other restaurant operating costs Other Cost and Expense, Operating General and administrative General and Administrative Expense Pre-opening Pre-Opening Costs Restaurant impairments, closure costs and asset disposals Total costs and expenses Costs and Expenses Loss from operations Operating Income (Loss) Interest expense, net Interest Expense Loss before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Net loss Accretion of preferred stock to redemption value Preferred Stock Dividends and Other Adjustments Net loss attributable to common stockholders Loss per share of Class A and Class B common stock, combined: Basic (USD per share) Diluted (USD per share) Weighted average shares of Class A and Class B common stock outstanding, combined: Weighted Average Number of Shares Outstanding, Diluted [Abstract] Basic (in shares) Diluted (in shares) Impaired Assets to be Disposed of by Method Other than Sale Impaired Assets to be Disposed of by Method Other than Sale [Table Text Block] Fair Value Disclosures [Abstract] Fair Value Measurements Fair Value Disclosures [Text Block] Business Summary and Basis of Presentation Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block]