CONDENSED 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	$ (67,180)	$ (84,482)	$ (61,889)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	34,389	28,791	16,749
Depreciation	3,348	2,757	2,215
Amortization of intangible assets	616	870	1,430
Amortization of premium (accretion) of investment securities	(14)	368
Provision for doubtful accounts	77	150	54
Loss on disposal of equipment	99		21
Changes in operating assets and liabilities:
Accounts receivable	(1,158)	(8,148)	(10,605)
Other current and noncurrent assets	(447)	(932)	(835)
Accounts payable	(1,297)	1,414	(12)
Accrued expenses and other long-term liabilities	1,637	(5,024)	2,881
Deferred revenue	18,201	15,701	13,422
Net cash used in operating activities	(11,729)	(48,535)	(36,569)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment	(2,930)	(3,730)	(3,119)
Proceeds from maturities of investment securities	94,631	44,964
Purchase of investment securities	(79,134)	(60,913)	(36,104)
Purchase of intellectual property			(650)
Net cash provided by (used in) investing activities	12,567	(19,679)	(39,873)
CASH FLOWS FROM FINANCING ACTIVITIES:
Amount drawn from revolving line of credit			3,300
Repayments of revolving line of credit			(7,600)
Proceeds from the issuance of convertible preferred stock-net of cash issuance costs			1,994
Proceeds from initial public offering			106,950
Payment of offering costs related to initial public offering			(4,076)
Proceeds from Employee Stock Purchase Plan	4,332	5,406	4,280
Proceeds from exercise of stock options	1,639	5,755	2,308
Net cash provided by financing activities	5,971	11,161	107,156
NET CHANGE IN CASH AND CASH EQUIVALENTS	6,809	(57,053)	30,714
CASH AND CASH EQUIVALENTS-Beginning of period	47,234	104,287	73,573
CASH AND CASH EQUIVALENTS-End of period	54,043	47,234	104,287
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Cash paid for income taxes	1,021	595	271
SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING ACTIVITIES RELATED TO ACQUISITIONS
Fair value of assets acquired			2,276
Liabilities assumed			(294)
Issuance of common stock			(1,982)
SUPPLEMENTAL DISCLOSURES OF NONCASH FINANCING ACTIVITIES:
Value of shares issued under the 2015 Non-Executive Bonus Plan	5,639
Value of shares issued under the Employee Stock Purchase Plan	$ 4,851	7,359
Purchase of property and equipment recorded in accounts payable		554
Tenant improvement allowance recorded in property and equipment and liabilities		$ 1,068
Offering costs recorded in accrued liabilities			$ 27