CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (48,442)	$ (56,974)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	26,249	26,666
Depreciation	2,430	2,540
Amortization of intangible assets	445	462
Provision for doubtful accounts	97	24
Amortization (accretion) of premium on investment securities	(36)	44
Changes in operating assets and liabilities:
Accounts receivable	(4,075)	970
Other current and noncurrent assets	(573)	(1,401)
Accounts payable	1,241	(944)
Accrued expenses and other long-term liabilities	2,362	119
Deferred revenue	12,937	8,297
Net cash used in operating activities	(7,365)	(20,197)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment	(5,046)	(2,349)
Proceeds from maturities of investment securities	35,415	70,717
Purchase of investment securities	(1,794)	(61,383)
Net cash provided by investing activities	28,575	6,985
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from Employee Stock Purchase Plan	3,590	3,247
Proceeds from exercise of stock options	3,911	814
Taxes paid for net settlement of stock-settled bonus	(3,149)
Net cash provided by financing activities	4,352	4,061
NET CHANGE IN CASH AND CASH EQUIVALENTS	25,562	(9,151)
CASH AND CASH EQUIVALENTS-Beginning of period	54,043	47,234
CASH AND CASH EQUIVALENTS-End of period	79,605	38,083
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Cash paid for income taxes	758	817
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 2016 Bonus Plans	5,123
Value of shares issued under the Employee Stock Purchase Plan	4,562	$ 4,851
Unpaid property and equipment purchases	$ 667