Summary of Significant Accounting Policies - Additional Information (Details)			1 Months Ended	12 Months Ended
	Sep. 15, 2020 USD ($) $ / shares shares	May 15, 2020 $ / shares shares	Oct. 31, 2020	Dec. 31, 2020 USD ($) ReportableSegment	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2020 USD ($)	Jan. 01, 2020 USD ($)	Jan. 01, 2018 USD ($)
Accounting Policies [Line Items]
Cash deposits included in restricted cash				$ 33,826,000	$ 1,853,000
Number of reporting units | ReportableSegment				3
Goodwill impairment				$ 0	0	$ 0
Deferred offering costs	$ 1,500,000
Common stock, issued | shares	10,800,000
Sale of stock, price per share | $ / shares	$ 54.50
Accumulated deficit				(777,871,000)	(573,860,000)
Operating lease liabilities				18,145,000				$ 18,400,000
Operating lease right-of-use assets				$ 17,137,000				$ 17,400,000
Topic 606
Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]				true
Change in accounting principle, accounting standards update, adoption date				Jan. 01, 2018
ASU 2018-15
Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]				true
Change in accounting principle, accounting standards update, adoption date				Jan. 01, 2019
Change in accounting principle, accounting standards update, immaterial effect [true false]				false
Capitalized implementation costs					2,700,000
Amortization expenses					$ 300,000
Topic 842
Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]				true
Change in accounting principle, accounting standards update, adoption date				Jan. 01, 2020
Change in accounting principle, accounting standards update, immaterial effect [true false]				false
ASU 2018-13
Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]				true
Change in accounting principle, accounting standards update, adoption date				Jan. 01, 2020
Change in accounting principle, accounting standards update, immaterial effect [true false]				true
ASU 2016-13
Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]				true
Change in accounting principle, accounting standards update, adoption date				Jan. 01, 2020
Change in accounting principle, accounting standards update, immaterial effect [true false]				true
Cumulative Effect, Period of Adoption, Adjustment | Topic 606
Accounting Policies [Line Items]
Accumulated deficit									$ 1,700,000
Maximum | ASU 2018-15
Accounting Policies [Line Items]
Amortization term					5 years
Minimum [Member] | ASU 2018-15
Accounting Policies [Line Items]
Amortization term					2 years
RA Agreement
Accounting Policies [Line Items]
Common stock, issued | shares		183,870
Term for issuance of additional shares of common stock		4 years
Sale of stock, price per share | $ / shares		$ 11.57
RA Agreement | Maximum
Accounting Policies [Line Items]
Issuance of additional shares of common stock | shares		8,641,914
Selling, General and Administrative Expenses
Accounting Policies [Line Items]
Advertising expense				$ 62,400,000	$ 49,900,000	25,600,000
Selling, General and Administrative Expenses | Shipping and Handling
Accounting Policies [Line Items]
Shipping and handling expenses				30,300,000	14,000,000	$ 6,400,000
Other Assets
Accounting Policies [Line Items]
Deferred offering costs				0	$ 2,400,000
Vehicle Floorplan Facilities | Line Of Credit
Accounting Policies [Line Items]
Increased borrowing capacity							$ 450,000,000
Amended to extend maturity date			2022-09
Vehicle Floorplan Facilities | Cash Deposits
Accounting Policies [Line Items]
Cash deposits included in restricted cash				$ 31,600,000