Summary of Significant Accounting Policies - Narrative (Details)	12 Months Ended
Jan. 31, 2021 USD ($) segment	Feb. 02, 2020 USD ($)	Feb. 03, 2019 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounts receivable	$ 100,699,000	$ 80,478,000
Impairment charges	0	0	$ 0
Fulfillment costs	871,000,000.0	546,200,000	403,900,000
Merchant processing fees	$ 146,000,000.0	$ 101,000,000.0	$ 74,100,000
Number of operating segments \| segment	1
Number of reportable segments \| segment	1
Products from three largest vendors \| Revenue Benchmark \| Product Concentration Risk
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Concentration risk percentage	32.60%	32.50%	30.10%
Customer Receivables
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounts receivable	$ 81,100,000	$ 58,300,000
Vendor Receivables
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounts receivable	$ 19,600,000	$ 22,200,000

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Amount, after allowance for credit loss, of right to consideration from customer for product sold and service rendered in normal course of business, classified as current.

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Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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