Property and Equipment, Net (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Property and Equipment [Line Items]
Total property and equipment	$ 193,244		$ 193,244		$ 175,096
Accumulated depreciation and amortization expenses	(111,670)		(111,670)		(88,856)
Total property and equipment, net	81,574		81,574		86,240
Depreciation expense	7,400	$ 7,300	22,800	$ 21,200
Capitalized computer software, amortization	6,700	6,200	20,000	17,800
Computer hardware
Property and Equipment [Line Items]
Total property and equipment	20,542		20,542		18,866
Furniture and equipment
Property and Equipment [Line Items]
Total property and equipment	3,546		3,546		3,559
Internal-use software development costs
Property and Equipment [Line Items]
Total property and equipment	153,576		153,576		137,085
Total property and equipment, net	71,700		71,700		75,300
Capitalized computer software additions	5,400	$ 5,600	16,500	$ 19,300
Leasehold improvements
Property and Equipment [Line Items]
Total property and equipment	$ 15,580		$ 15,580		$ 15,586