Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)			1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 15, 2020	May 15, 2020	Oct. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Accounting Policies [Line Items]
Cash deposits included in restricted cash				$ 27,961,000		$ 27,961,000				$ 1,853,000
Common stock, issued	10,800,000
Sale of stock, price per share	$ 54.50
Operating lease liabilities				15,295,000		15,295,000			$ 18,400,000
Operating lease right-of-use assets				$ 14,337,000		$ 14,337,000			$ 17,400,000
Topic 842
Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]				true		true
Change in accounting principle, accounting standards update, adoption date				Jan. 01, 2020		Jan. 01, 2020
Change in accounting principle, accounting standards update, immaterial effect [true false]				false		false
ASU 2018-13
Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]				true		true
Change in accounting principle, accounting standards update, adoption date				Jan. 01, 2020		Jan. 01, 2020
Change in accounting principle, accounting standards update, immaterial effect [true false]				true		true
ASU 2016-13
Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]				true		true
Change in accounting principle, accounting standards update, adoption date				Jan. 01, 2020		Jan. 01, 2020
Change in accounting principle, accounting standards update, immaterial effect [true false]				true		true
RA Agreement
Accounting Policies [Line Items]
Common stock, issued		183,870
Term for issuance of additional shares of common stock		4 years
Sale of stock, price per share		$ 11.57
RA Agreement | Maximum
Accounting Policies [Line Items]
Issuance of additional shares of common stock		8,641,914
Selling, General and Administrative Expenses
Accounting Policies [Line Items]
Advertising expense				$ 15,300,000	$ 14,600,000	$ 44,800,000	$ 34,400,000
Selling, General and Administrative Expenses | Shipping and Handling
Accounting Policies [Line Items]
Shipping and handling expenses				8,500,000	$ 4,300,000	19,800,000	$ 9,200,000
Vehicle Floorplan Facilities | Line Of Credit
Accounting Policies [Line Items]
Increased borrowing capacity								$ 450,000,000
Vehicle Floorplan Facilities | Line Of Credit | Subsequent Event
Accounting Policies [Line Items]
Amended to extend maturity date			2022-09
Vehicle Floorplan Facilities | Cash Deposits
Accounting Policies [Line Items]
Cash deposits included in restricted cash				$ 26,100,000		$ 26,100,000