Summary of Significant Accounting Policies - Narrative (Details)	12 Months Ended
	Feb. 02, 2020 USD ($) segment	Feb. 03, 2019 USD ($)	Jan. 28, 2018 USD ($)	Feb. 04, 2019 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounts receivable	$ 80,478,000	$ 48,738,000
Impairment charges	0	0	$ 0
Fulfillment costs	546,200,000	403,900,000	258,900,000
Merchant processing fees	$ 101,000,000.0	$ 74,100,000	$ 45,200,000
Number of operating segments | segment	1
Number of reportable segments | segment	1
Operating lease right-of-use assets	$ 179,052,000
Operating lease liabilities	$ 215,930,000
Products from three largest vendors | Revenue Benchmark | Product Concentration Risk
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Concentration risk percentage	32.50%	30.10%	28.50%
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets				$ 162,800,000
Operating lease liabilities				$ 193,600,000
Customer Receivables
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounts receivable	$ 58,300,000	$ 41,500,000
Vendor Receivables
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounts receivable	$ 22,200,000	$ 7,200,000