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 loss	$ (31,553)	$ (41,007)	$ (32,872)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	5,988	6,486	5,229
Amortization of premiums on investments	38	87	228
Loss (gain) on disposal of property and equipment	25	(9)
Stock-based compensation	10,459	7,815	5,766
Accretion of capitalized loan fees	136	62	18
Loss on extinguishment of debt	722
Remeasurement of preferred stock warrant liability	202	57	116
Foreign exchange loss	412
Change in operating assets and liabilities
Accounts receivable	(5,765)	(6,193)	(15,201)
Prepaid expenses and other assets	(3,606)	(970)	(2,009)
Accounts payable	278	666	1,407
Accrued expenses	1,626	2,095	2,473
Deferred revenue	16,908	19,936	17,031
Deferred rent	136	384	(143)
Net cash used in operating activities	(3,994)	(10,591)	(17,957)
Cash flows from investing activities
Purchases of property and equipment	(5,402)	(7,643)	(6,319)
Proceeds from maturities of investments	6,245	16,839	28,385
Purchases of investments	(75,303)	(2,715)	(20,744)
(Payment) return of security deposits	(184)	177	(716)
Net cash (used in) provided by investing activities	(74,644)	6,658	606
Cash flows from financing activities
Proceeds from initial public offering, net of underwriting discounts	102,672
Payment of initial public offering costs	(2,362)	(1,092)
Proceeds from long-term debt	20,000
Principal payments on long-term debt	(20,000)
Payment of debt prepayment fees	(200)
Proceeds from exercise of common stock options	1,333	2,670	1,437
Principal payments on capital lease obligations	(43)	(45)	(41)
Payment of capitalized loan fees	(248)	(78)
Net cash provided by financing activities	101,152	1,455	1,396
Foreign currency effect on cash, cash equivalents and restricted cash	(263)	(37)	(90)
Net increase (decrease) in cash, cash equivalents and restricted cash	22,251	(2,515)	(16,045)
Cash, cash equivalents and restricted cash
Beginning of year	19,756	22,271	38,316
End of year	42,007	19,756	22,271
Supplemental disclosures
Cash paid for interest	771	13	18
Purchases under capital lease obligations		102	4
Property and equipment additions in accounts payable and accrued expenses	639	234	2,970
Leasehold improvements paid directly by lessor	356		$ 1,268
Non-cash warrants issued as debt issuance costs	285	90
Initial public offering costs in accounts payable and accrued expenses	244	$ 881
Non-cash preferred stock warrant exercise	$ 616