Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities
Net loss		$ (17,966)	$ (18,163)	[1]
Adjustments to reconcile net loss to net cash provided by operating activities
Depreciation and amortization		4,000	4,657	[1]
(Accretion of discounts)/amortization of premiums on investments		(517)	59	[1]
Amortization of acquisition-related intangible assets		2,388
Amortization of deferred costs		12,222	10,093	[1]
Amortization of debt discount and issuance costs		3,362	18	[1]
Loss on disposal of property and equipment		9	7	[1]
Stock-based compensation		16,686	11,667	[1]
Foreign exchange loss (gain)		797	(159)	[1]
Change in operating assets and liabilities, net of impact of business combination
Accounts receivable		7,986	12,026	[1]
Prepaid expenses and other assets		(593)	3,260	[1]
Deferred costs		(13,611)	(10,648)	[1]
Accounts payable		1,104	635	[1]
Accrued expenses		2,437	(2,025)	[1]
Deferred revenue		(9,871)	72	[1]
Deferred rent		(594)	(596)	[1]
Net cash provided by operating activities		7,839	10,903	[1]
Cash flows from investing activities
Business combination, net of cash acquired		(39,041)
Purchases of property and equipment		(2,238)	(2,837)	[1]
Proceeds from sales of equipment		38	11	[1]
Proceeds from maturities of investments		115,950	35,075	[1]
Purchases of investments		(101,785)	(66,196)	[1]
Return of (payments for) security deposits		53	(23)	[1]
Net cash used in investing activities		(27,023)	(33,970)	[1]
Cash flows from financing activities
Proceeds from borrowings on convertible notes, net of discounts		139,438
Purchase of capped calls		(17,092)
Proceeds from exercises of common stock options		18,032	8,948	[1]
Payment of issuance costs on convertible notes		(469)
Proceeds from purchases of stock under employee stock purchase plan		2,391	2,251	[1]
Payment of initial public offering costs	[1]		(243)
Principal payments on capital lease obligations		(20)	(32)	[1]
Net cash provided by financing activities		142,280	10,924	[1]
Foreign currency effect on cash, cash equivalents and restricted cash		(488)	(585)	[1]
Net increase (decrease) in cash, cash equivalents and restricted cash		122,608	(12,728)	[1]
Cash, cash equivalents and restricted cash
Beginning of period		55,069	42,007	[1]
End of period		177,677	29,279	[1]
Supplemental non-cash disclosures
Purchases under capital lease obligations		144
Property and equipment additions in accounts payable and accrued expenses		1,842	$ 328	[1]
Leasehold improvements paid directly by lessor		218
Class A Common Stock
Supplemental non-cash disclosures
Class A Common stock issued in business combination		$ 4,617

[1] See Note 1 for a summary of adjustments