Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net loss	$ (45,470)	$ (49,000)	$ (49,857)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	7,628	6,725	5,352
Amortization of debt discount	0	0	1,129
Stock-based compensation expense	19,541	17,316	10,685
Provision for doubtful accounts	905	931	828
Impairment of long-lived assets	0	0	483
Deferred income taxes	(2,860)	75	119
Foreign currency re-measurement (gain) loss	(364)	58	153
Other non-cash expenses	209	222	209
Changes in assets and liabilities:
Accounts receivable	(25,217)	(6,195)	(18,370)
Prepaid expenses and other assets	(74)	(3,523)	(1,787)
Accounts payable	(2,257)	1,619	(2,302)
Accrued expenses	6,758	1,578	6,702
Deferred revenue	55,437	38,748	44,868
Other liabilities	(950)	558	(119)
Net cash provided by (used in) operating activities	13,286	9,112	(1,907)
Cash flows from investing activities:
Business acquisitions, net of cash acquired	(14,717)	0	(38,811)
Purchases of property and equipment	(4,824)	(4,499)	(4,136)
Capitalization of internal-use software	(1,162)	0	0
Purchases of investments	(35,190)	(38,976)	0
Sales and maturities of investments	33,672	0	0
Increase in restricted cash	(200)	0	0
Net cash used in investing activities	(22,421)	(43,475)	(42,947)
Cash flows from financing activities:
Proceeds from initial public offering and concurrent private placement, net of offering costs of $3,097	0	0	112,275
Repayments of term loan and related termination fee	0	0	(18,540)
Deferred business acquisition payment	(796)	(1,392)	0
Payments of capital lease obligations	0	(68)	(253)
Taxes paid related to net share settlement of equity awards	(698)	(4,114)	0
Excess tax benefit from stock-based compensation	0	87	0
Proceeds from employee stock purchase plan	2,914	3,724	0
Proceeds from stock option exercises	5,848	2,924	1,304
Net cash provided by financing activities	7,268	1,161	94,786
Effect of exchange rate changes on cash and cash equivalents	281	(203)	(202)
Net (decrease) increase in cash and cash equivalents	(1,586)	(33,405)	49,730
Cash and cash equivalents, beginning of period	53,148	86,553	36,823
Cash and cash equivalents, end of period	51,562	53,148	86,553
Supplemental cash flow information:
Cash paid for income taxes	801	556	341
Cash paid for interest	0	5	1,427
Supplemental non-cash investing and financing information:
Common stock issued for acquisitions	0	0	27,481
Vested stock options issued for acquisition	$ 0	$ 0	$ 4,494