Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)		1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	May 15, 2020	Mar. 31, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Jan. 01, 2020
Accounting Policies [Line Items]
Cash deposits included in restricted cash			$ 21,853,000		$ 21,853,000		$ 1,853,000
Proceeds from issuance of IPO					504,023,000
Under writing discount and offering expenses					7,500,000
Operating lease liabilities			16,390,000		16,390,000			$ 18,400,000
Operating lease right-of-use assets			15,437,000		15,437,000			$ 17,400,000
Annual revenue exceeded							$ 1,070,000,000
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			11,600,000	$ 12,700,000	29,500,000	$ 19,800,000
Selling, General and Administrative Expenses | Shipping and Handling
Accounting Policies [Line Items]
Shipping and handling expenses			5,500,000	$ 2,700,000	11,300,000	$ 4,900,000
Vehicle Floorplan Facilities | Line Of Credit
Accounting Policies [Line Items]
Increased borrowing capacity		$ 450,000,000
Extended term		2021-03
Vehicle Floorplan Facilities | Cash Deposits
Accounting Policies [Line Items]
Cash deposits included in restricted cash			$ 20,000,000		$ 20,000,000