CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
OPERATING ACTIVITIES:
Net income	$ 137,762	$ 242,317	$ 108,318
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	42,219	28,632	21,662
Stock-based compensation	337,413	111,775	80,758
Deferred income taxes	(16,777)	(31,218)	(10,490)
Allowance for credit losses on accounts receivable	1,456	3,149	2,702
Noncash lease expense	40,315	33,269	21,894
Other	5,803	2,190	(1,939)
Changes in operating assets and liabilities:
Accounts receivable	(444,342)	(418,054)	(331,369)
Prepaid expenses and other assets	1,648	(66,655)	(19,597)
Accounts payable	309,410	481,313	191,763
Accrued expenses and other liabilities	7,596	35,446	6,845
Operating lease liabilities	(43,990)	(17,095)	(10,342)
Net cash provided by operating activities	378,513	405,069	60,205
INVESTING ACTIVITIES:
Purchases of investments	(278,387)	(230,759)	(212,776)
Sales of investments	4,539
Maturities of investments	253,444	167,602	89,539
Purchases of property and equipment	(54,804)	(74,061)	(35,693)
Capitalized software development costs	(5,169)	(6,053)	(4,911)
Business acquisition	(13,261)
Net cash used in investing activities	(93,638)	(143,271)	(163,841)
FINANCING ACTIVITIES:
Proceeds from line of credit		143,000
Repayment on line of credit		(143,000)
Payment of debt financing costs	(1,924)		(6)
Proceeds from exercise of stock options	61,476	76,146	29,874
Proceeds from employee stock purchase plan	29,229	21,671	16,746
Taxes paid related to net settlement of restricted stock awards	(56,855)	(53,138)	(19,334)
Net cash provided by financing activities	31,926	44,679	27,280
Increase (decrease) in cash and cash equivalents	316,801	306,477	(76,356)
Cash and cash equivalents—Beginning of year	437,353	130,876	207,232
Cash and cash equivalents—End of year	754,154	437,353	130,876
SUPPLEMENTAL CASH FLOW INFORMATION:
Cash paid for income taxes	3,608	4,983	19,727
Cash paid for interest	518	1,554	412
Cash paid for operating lease liabilities	52,974	27,448	16,923
Asset retirement obligation	1,705	2,049	3,543
Operating lease assets obtained in exchange for operating lease liabilities	25,356	106,833	150,467
Capitalized assets financed by accounts payable	5,907	6,766	9,252
Stock-based compensation included in capitalized software development costs	$ 3,320	$ 2,245	$ 1,588