Unaudited Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Cash flows from operating activities
Net income	$ 116,894	$ 91,604
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	30,933	25,290
Accretion of discount on available-for-sale securities	(183)	(974)
Non-cash marketing expense	157
Loss on disposition of property and equipment	132
Amortization of debt issuance costs	18	19
Stock-based compensation expense	47,373	37,029
Cash paid for derivative settlement	(418)	(233)
(Gain)/loss on derivative	(287)	1,939
Deferred income taxes, net	6,485	7,319
Changes in operating assets and liabilities:
Accounts receivable	(10,775)	3
Prepaid expenses	(14,430)	(11,426)
Inventory	80	(433)
Other assets	1,631	(1,113)
Deferred contract costs	(44,893)	(40,488)
Accounts payable	2,267	(1,017)
Income taxes, net	2,450	(304)
Accrued commissions and bonuses	(3,785)	(5,804)
Accrued payroll and vacation	4,111	4,079
Deferred revenue	5,632	4,643
Accrued expenses and other current liabilities	3,051	(2,621)
Net cash provided by operating activities	146,443	107,512
Cash flows from investing activities
Purchase of short-term investments from funds held for clients	(142,051)	(207,878)
Proceeds from maturities of short-term investments from funds held for clients	155,000	70,343
Purchases of property and equipment	(62,732)	(52,458)
Net cash used in investing activities	(49,783)	(189,993)
Cash flows from financing activities
Repurchases of common stock		(52,040)
Withholding taxes paid related to net share settlements	(32,355)	(23,249)
Payments on long-term debt	(888)	(888)
Net change in client funds obligation	411,878	(629,243)
Net cash provided by (used in) financing activities	378,635	(705,420)
Increase (decrease) in cash, cash equivalents, restricted cash and restricted cash equivalents	475,295	(787,901)
Cash, cash equivalents, restricted cash and restricted cash equivalents
Cash, cash equivalents, restricted cash and restricted cash equivalents, beginning of period	1,585,275	1,641,854
Cash, cash equivalents, restricted cash and restricted cash equivalents, end of period	2,060,570	853,953
Cash and cash equivalents	202,362	113,518
Restricted cash included in funds held for clients	1,858,208	740,435
Non-cash investing and financing activities:
Purchases of property and equipment, accrued but not paid	7,131	4,832
Stock-based compensation for capitalized software	3,351	3,718
Right of use assets obtained in exchange for operating lease liabilities	$ 1,572	$ 5,124