Organization and Summary of Significant Accounting Policies - Narrative (Details)						1 Months Ended	3 Months Ended		6 Months Ended
	May 28, 2020 shares	Apr. 27, 2020 USD ($) shares	Feb. 03, 2020 USD ($) shares	Oct. 08, 2019 USD ($) shares	Jun. 24, 2019 USD ($) $ / shares shares	Jun. 29, 2019 USD ($) store $ / shares shares	Jun. 27, 2020 USD ($) store $ / shares shares	Jun. 29, 2019 USD ($) store $ / shares	Jun. 27, 2020 USD ($) store $ / shares shares	Jun. 29, 2019 USD ($) store $ / shares	Mar. 28, 2020 USD ($)	Dec. 29, 2019 USD ($)	Dec. 28, 2019 USD ($) store $ / shares shares	Mar. 30, 2019 USD ($)	Dec. 29, 2018 USD ($)
Subsidiary, Sale of Stock [Line Items]
Number of stores | store							362		362
Proceeds from initial public offering, net of underwriting discounts paid									$ 0	$ 407,666,000
Conversion rate					1
Common stock, shares authorized (in shares) | shares					500,000,000		500,000,000		500,000,000				500,000,000
Preferred stock, shares authorized (in shares) | shares					50,000,000		50,000,000		50,000,000				50,000,000
Preferred stock, par (in usd per share) | $ / shares					$ 0.001		$ 0.001		$ 0.001				$ 0.001
Redemption of preferred stock								$ 0
Deferred offering cost		$ 1,000,000.0	$ 1,100,000
Proceeds from stock option exercised		$ 1,600,000	$ 1,400,000
Options exercised (in shares) | shares		269,000	191,470
Number of reportable segments (in segments) | store									1
Number of operating segments (in segments) | store									1
Gift card, redemption period									12 months
Contract with customer, liability							$ 1,800,000		$ 1,800,000				$ 2,000,000.0
Variable interest entity, number of stores | store						324	357	324	357	324			342
Net sales							$ 803,429,000	$ 645,289,000	$ 1,563,737,000	$ 1,251,560,000
Liabilities							1,490,892,000		$ 1,490,892,000				$ 1,440,145,000
Accounting Standards Update [Extensible List]									us-gaap:AccountingStandardsUpdate201613Member
Effect on stockholder's equity						$ 716,688,000	833,401,000	716,688,000	$ 833,401,000	716,688,000	$ 784,628,000		745,384,000	$ 303,851,000	$ 299,951,000
Hellman and Friedman, LLC [Member]
Subsidiary, Sale of Stock [Line Items]
Transfer of common stock holdings to stockholder's equity holders (in shares) | shares	9,600,000
Variable Interest Entity, Not Primary Beneficiary
Subsidiary, Sale of Stock [Line Items]
Net sales							788,500,000	629,700,000	1,530,000,000	1,220,000,000
Sales commissions and fees							122,500,000	95,800,000	236,900,000	187,000,000.0
Liabilities							9,400,000		9,400,000				6,100,000
Maximum loss exposure							40,600,000		40,600,000				37,700,000
Cumulative Effect, Period of Adoption, Adjustment
Subsidiary, Sale of Stock [Line Items]
Effect on stockholder's equity													439,000		169,000
Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjustment
Subsidiary, Sale of Stock [Line Items]
Effect on stockholder's equity												$ 400,000
Preferred Stock
Subsidiary, Sale of Stock [Line Items]
Redemption of preferred stock					$ 1.00			0
Effect on stockholder's equity						$ 0	$ 0	$ 0	$ 0	$ 0	$ 0		$ 0	$ 0	$ 0
Senior Notes | Second Lien Credit Agreement
Subsidiary, Sale of Stock [Line Items]
Repayments of long-term debt					150,000,000.0
Debt instrument, periodic payment, interest					3,600,000
Senior Notes | First Lien Credit Agreement
Subsidiary, Sale of Stock [Line Items]
Repayments of long-term debt					248,000,000.0
Debt instrument, periodic payment, interest					$ 3,800,000
IPO
Subsidiary, Sale of Stock [Line Items]
Issuance of common stock upon initial public offering, net of issuance costs (in shares) | shares				451,470		19,765,625
Sale of stock (in usd per share) | $ / shares						$ 22.00		$ 22.00		$ 22.00
Proceeds from initial public offering, net of underwriting discounts paid				$ 3,200,000		$ 407,700,000
Underwriting discounts and commissions						27,100,000
Payments of stock issuance costs				$ 1,100,000		$ 7,200,000