Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities
Net income	$ 41,160	$ 33,694
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	6,069	4,286
Amortization of debt issuance costs	6	23
Stock-based compensation expense	23,222	3,343
Cash paid for derivative settlement	(79)
Gain on derivative	(738)
Deferred income taxes, net	4,272	1,285
Changes in operating assets and liabilities:
Accounts receivable	(774)	(508)
Prepaid expenses	(2,019)	(938)
Inventory	(193)	176
Deposits and other assets	(565)	(154)
Deferred contract costs	(17,712)	(13,563)
Accounts payable	(710)	(1,349)
Income taxes, net	4,013	17,269
Accrued commissions and bonuses	(6,980)	(5,277)
Accrued payroll and vacation	4,307	2,919
Deferred revenue	2,153	2,455
Accrued expenses and other current liabilities	2,232	(3,436)
Net cash provided by operating activities	57,664	40,225
Cash flows from investing activities
Net change in funds held for clients	(5,959)	(92,736)
Purchases of property and equipment	(18,708)	(9,136)
Net cash provided by investing activities	(24,667)	(101,872)
Cash flows from financing activities
Proceeds from issuance of long-term debt		2,093
Repurchases of common stock	(4,999)
Withholding taxes paid related to net share settlement	(11,871)
Principal payments on long-term debt		(282)
Net change in client funds obligation	5,959	92,736
Payment of debt issuance costs	(42)	(143)
Net cash (used in) provided by financing activities	(10,953)	94,404
Increase in cash and cash equivalents	22,044	32,757
Cash and cash equivalents
Beginning of period	46,077	60,158
End of period	$ 68,121	$ 92,915