Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net loss	$ (14,134)	$ (12,342)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization	3,705	2,638
Amortization of deferred costs	1,598	1,233
Loss on disposal of assets		84
Deferred income taxes	41	34
Accretion of interest on convertible senior notes	1,201	1,134
Non-cash investment income	(189)	(159)
Provision for (benefit from) doubtful accounts and sales reserve	148	(192)
Stock-based compensation	7,785	6,586
Changes in operating assets and liabilities:
Accounts receivable	5,543	9,595
Prepaid expenses	(4,233)	(1,651)
Deferred costs	(2,227)	(2,223)
Other assets	2,153	(2,018)
Accounts payable	4,112	702
Accrued payroll and employee related liabilities	1,205	4,402
Accrued expenses	(1,065)	1,384
Deferred revenue	2,767	(2,072)
Other liabilities	277	373
Net cash provided by operating activities	8,687	7,508
Cash flows from investing activities:
Capital expenditures	(2,773)	(253)
Purchase of cost investment		(308)
Purchase of short-term investments	(1,975)	(30,932)
Maturities of short-term investments	24,750	25,500
Additions to intangibles		(136)
Additions to capitalized software development costs	(2,018)	(1,999)
Net cash provided by (used in) investing activities	17,984	(8,128)
Cash flows from financing activities:
Restricted stock units withheld to settle employee tax withholding liability	(333)	(1,022)
Proceeds from public offering, net of costs	139,115
Payments on note payable	(52)
Payments on finance lease obligations	(121)
Payments of debt issuance costs		(84)
Proceeds from employee stock purchase plan	1,283	881
Proceeds from stock option exercises	8,746	1,466
Net cash provided by financing activities	148,638	1,241
Effect of exchange rates on cash, cash equivalents and restricted cash	(28)	(39)
Net increase in cash, cash equivalents and restricted cash	175,281	582
Cash, cash equivalents and restricted cash—beginning of period	60,068	103,051
Cash, cash equivalents and restricted cash—end of period	235,349	103,633
Supplemental disclosures of cash flow information:
Taxes, net of refunds received		2
Supplemental disclosure of non-cash activities:
Capitalized assets included in accounts payable and accrued expenses	689	38
Capitalized development costs included in accounts payable and accrued expenses	16
Stock-based compensation capitalized for software development	$ 64	$ 108