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	$ (70,279)	$ (48,882)	$ (59,176)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization	7,488	4,551	3,578
Stock-based compensation	62,875	50,964	37,273
Amortization of acquired intangibles	1,408	1,408	1,269
Amortization of premiums/accretion of discounts on short-term investments	238	496	416
Loss on disposal of equipment	267	0	0
Excess tax benefits from share-based compensation	(36)	(165)	(385)
Other	125	0	0
Changes in operating assets and liabilities:
Accounts receivable, net	(1,520)	(13,605)	(3,000)
Inventory	(16)	(1,056)	253
Prepaid expenses and other assets	383	(4,220)	409
Accounts payable	(1,398)	977	1,150
Accrued compensation and benefits	(2,543)	4,510	2,630
Accrued and other liabilities	2,178	3,242	1,847
Severance pay, net	272	16	93
Deferred revenue	23,684	25,482	18,123
Deferred tax assets	(632)	149	(354)
Net cash provided by operating activities	22,494	23,867	4,126
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of short-term investments	(129,989)	(89,626)	(33,267)
Proceeds from sales/maturities of short-term investments	72,453	33,948	29,821
Acquisitions, net of cash acquired	(3,914)	0	(12,083)
Net purchases of property and equipment	(16,789)	(8,080)	(5,621)
Change in restricted cash	(208)	(17)	(441)
Net cash used in investing activities	(78,447)	(63,775)	(21,591)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from follow-on public offering, net of offering costs	0	127,853	0
Settlement of holdback liability	(7,157)	0	0
Proceeds from issuance of common stock, net of repurchases	11,233	23,524	10,546
Shares withheld for tax withholding on vesting of restricted stock units	(8,831)	(11,464)	(2,074)
Offering costs relating to follow-on public offering	(112)	0	0
Excess tax benefits from share-based compensation	36	165	385
Net cash (used in) provided by financing activities	(4,831)	140,078	8,857
Effect of exchange rate changes on cash and cash equivalents	(125)	(14)	0
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(60,909)	100,156	(8,608)
CASH AND CASH EQUIVALENTS - Beginning of period	168,252	68,096	76,704
CASH AND CASH EQUIVALENTS - End of period	107,343	168,252	68,096
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Cash paid for income taxes	1,480	652	287
NONCASH INVESTING AND FINANCING ACTIVITIES:
Common stock issued related to acquisitions of businesses	0	0	24,163
Property and equipment incurred but not yet paid	574	517	820
Vesting of restricted and early exercised stock options	$ 0	$ 767	$ 454