CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net loss	$ (55,545,000)	$ (45,470,000)	$ (49,000,000)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization	11,097,000	7,628,000	6,725,000
Amortization of debt discount and issuance costs	3,831,000	0	0
Stock-based compensation expense	27,593,000	19,541,000	17,316,000
Provision for doubtful accounts	740,000	905,000	931,000
Deferred income taxes	(69,000)	(2,860,000)	75,000
Foreign currency re-measurement (gain) loss	757,000	(364,000)	58,000
Other non-cash items	(506,000)	209,000	222,000
Changes in assets and liabilities:
Accounts receivable	(1,685,000)	(25,217,000)	(6,195,000)
Deferred contract acquisition and fulfillment costs	(12,790,000)	0	0
Prepaid expenses and other assets	(287,000)	(74,000)	(3,523,000)
Accounts payable	3,675,000	(2,257,000)	1,619,000
Accrued expenses	6,018,000	6,758,000	1,578,000
Deferred revenue	22,870,000	55,437,000	38,748,000
Other liabilities	367,000	(950,000)	558,000
Net cash provided by operating activities	6,066,000	13,286,000	9,112,000
Cash flows from investing activities:
Business acquisitions, net of cash acquired	(14,460,000)	(14,717,000)	0
Purchases of property and equipment	(12,813,000)	(4,824,000)	(4,499,000)
Capitalization of internal-use software	(3,265,000)	(1,162,000)	0
Purchases of investments	(233,421,000)	(35,190,000)	(38,976,000)
Sales and maturities of investments	70,226,000	33,672,000	0
Net cash used in investing activities	(193,733,000)	(22,221,000)	(43,475,000)
Cash flows from financing activities:
Proceeds from issuance of convertible senior notes, net of issuance costs of $6,879	223,121,000	0	0
Purchase of capped calls related to convertible senior notes	(26,910,000)	0	0
Proceeds from secondary public offering, net of offering costs of $608	30,907,000	0	0
Deferred business acquisition payment	0	(796,000)	(1,392,000)
Payments of capital lease obligations	0	0	(68,000)
Taxes paid related to net share settlement of equity awards	(2,197,000)	(698,000)	(4,114,000)
Excess tax benefit from stock-based compensation	0	0	87,000
Proceeds from employee stock purchase plan	3,637,000	2,914,000	3,724,000
Proceeds from stock option exercises	7,606,000	5,848,000	2,924,000
Net cash provided by financing activities	236,164,000	7,268,000	1,161,000
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(694,000)	281,000	(203,000)
Net increase (decrease) in cash, cash equivalents and restricted cash	47,803,000	(1,386,000)	(33,405,000)
Cash, cash equivalents and restricted cash, beginning of period	51,762,000	53,148,000	86,553,000
Cash, cash equivalents and restricted cash, end of period	99,565,000	51,762,000	53,148,000
Supplemental cash flow information:
Cash paid for income taxes	188,000	801,000	556,000
Cash paid for interest	0	0	5,000
Reconciliation of cash, cash equivalents and restricted cash:
Total cash, cash equivalents and restricted cash	$ 51,762,000	$ 53,148,000	$ 86,553,000