Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash flows from operating activities
Net income	$ 281,389	$ 195,960	$ 143,453
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	92,699	67,222	53,373
Accretion of discount on available-for-sale securities	(1,020)	(452)	(1,563)
Non-cash marketing expense	1,734	1,051
(Gain)/loss on disposition of property and equipment	(150)	146
Amortization of debt issuance costs	847	36	36
Stock-based compensation expense	94,898	97,506	90,108
Cash paid for derivative settlement	205	(741)	(613)
(Gain)/loss on derivative	(1,559)	(662)	1,993
Deferred income taxes, net	(3,210)	32,906	21,381
Other	(206)
Changes in operating assets and liabilities:
Accounts receivable	(13,353)	(360)	168
Prepaid expenses	(6,497)	(5,875)	(4,293)
Inventory	(224)	481	(41)
Other assets	(13,907)	(7,862)	(1,720)
Deferred contract costs	(122,440)	(103,356)	(89,776)
Accounts payable	11,676	(660)	1,529
Income taxes, net	10,830	(5,966)	(6,427)
Accrued commissions and bonuses	6,082	8,654	1,360
Accrued payroll and vacation	10,764	9,730	9,659
Deferred revenue	15,990	14,600	10,582
Accrued expenses and other current liabilities	555	17,004	(2,002)
Net cash provided by operating activities	365,103	319,362	227,207
Cash flows from investing activities
Purchases of investments from funds held for clients	(268,718)	(398,819)	(332,756)
Proceeds from investments from funds held for clients	382,230	267,341	308,981
Purchases of intangible assets	(4,120)	(5,500)
Purchases of property and equipment	(132,678)	(120,692)	(94,102)
Net cash used in investing activities	(23,286)	(257,670)	(117,877)
Cash flows from financing activities
Proceeds from the issuance of debt	29,000
Repurchases of common stock	(94,652)		(52,040)
Withholding taxes paid related to net share settlements	(5,171)	(65,580)	(62,811)
Payments on long-term debt	(29,287)	(1,775)	(1,775)
Net change in client funds obligation	361,133	233,079	(49,283)
Payment of debt issuance costs	(6,436)
Net cash provided by (used in) financing activities	254,587	165,724	(165,909)
Increase (decrease) in cash, cash equivalents, restricted cash and restricted cash equivalents	596,404	227,416	(56,579)
Cash, cash equivalents, restricted cash and restricted cash equivalents
Cash, cash equivalents, restricted cash and restricted cash equivalents, beginning of period	1,812,691	1,585,275	1,641,854
Cash, cash equivalents, restricted cash and restricted cash equivalents, end of period	2,409,095	1,812,691	1,585,275
Cash and cash equivalents	400,730	277,978	151,710
Restricted cash included in funds held for clients	2,008,365	1,534,713	1,433,565
Supplemental disclosures of cash flow information:
Cash paid for interest, net of amounts capitalized	507	2
Cash paid for income taxes	100,578	33,068	27,530
Non-cash investing and financing activities:
Purchases of property and equipment, accrued but not paid	5,899	7,581	837
Stock-based compensation for capitalized software	8,965	7,141	6,655
Right of use assets obtained in exchange for operating lease liabilities	$ 21,467	$ 14,141	$ 9,693