Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net income	$ 43,840	$ 20,945	$ 5,663
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	13,632	9,421	7,162
(Gain)/loss on disposition of property and equipment	(64)	15
Amortization of debt discount and debt issuance costs	124	157	133
Write off of debt discount, net			4,051
Stock-based compensation expense	22,471	3,219	712
Net change in derivative liability			(1,107)
Deferred income taxes, net	(1,848)	(1,021)	2,259
Changes in operating assets and liabilities:
Accounts receivable	1,015	440	(1,089)
Prepaid expenses	(944)	(1,579)	(465)
Inventory	418	(224)	267
Deposits and other assets	71	(810)	(232)
Accounts payable	(1,571)	(431)	(2,386)
Income taxes, net	6,051	(5,808)	(122)
Accrued commissions and bonuses	(684)	3,607	1,482
Accrued payroll and vacation	1,871	1,316	(1,505)
Deferred revenue	10,675	9,699	6,765
Accrued expenses and other current liabilities	3,896	4,026	749
Net cash provided by operating activities	98,953	42,972	22,337
Cash flows from investing activities:
Increase in funds held for clients	(161,541)	(36,146)	(204,778)
Decrease (increase) in restricted cash		371	(2)
Purchases of property and equipment	(43,805)	(16,549)	(14,270)
Proceeds from sale of property and equipment	295
Net cash used in investing activities	(205,051)	(52,324)	(219,050)
Cash flows from financing activities:
Proceeds from issuance of long-term debt	5,000		6,538
Repurchases of common stock	(35,561)
Withholding taxes paid related to net share settlements	(14,396)
Principal payments on long-term debt	(964)	(1,118)	(65,650)
Increase in client funds obligation	161,541	36,146	204,778
Proceeds from initial public offering, net of offering costs			62,840
Payment of debt issuance costs	(78)	(106)	(11)
Net cash provided by financing activities	115,542	34,922	208,495
Net increase in cash and cash equivalents	9,444	25,570	11,782
Cash and cash equivalents
Beginning of year	50,714	25,144	13,362
End of year	60,158	50,714	25,144
Supplemental disclosures of cash flow information:
Cash paid for interest, net of amounts capitalized	938	1,271	3,482
Cash paid for income taxes	9,323	19,205	2,013
Noncash investing and financing activities:
Purchases of property and equipment, accrued but not paid	4,651	1,613	408
Stock-based compensation for capitalized software	$ 1,784	$ 220	$ 4