CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (12,833)	$ (19,447)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	6,547	8,249
Depreciation	788	868
Amortization of intangible assets	154	154
Amortization (accretion) of premium on investment securities	(30)	52
Changes in operating assets and liabilities:
Accounts receivable	5,682	11,020
Other current and noncurrent assets	(7,923)	(3,220)
Accounts payable	1,855	(424)
Accrued expenses and other long-term liabilities	3,398	(1,080)
Deferred revenue	3,086	282
Net cash provided by (used in) operating activities	724	(3,546)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment	(393)	(1,589)
Proceeds from maturities of investment securities	24,965	29,012
Purchase of investment securities		(23,933)
Net cash provided by investing activities	24,572	3,490
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from Employee Stock Purchase Plan	1,130	1,075
Proceeds from exercise of stock options	1,817	299
Taxes paid for net settlement of stock-settled bonus	(3,024)
Net cash (used in) provided by financing activities	(77)	1,374
NET CHANGE IN CASH AND CASH EQUIVALENTS	25,219	1,318
CASH AND CASH EQUIVALENTS-Beginning of period	54,043	47,234
CASH AND CASH EQUIVALENTS-End of period	79,262	48,552
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Cash paid for income taxes	241	231
SUPPLEMENTAL DISCLOSURES OF NONCASH FINANCING ACTIVITIES:
Value of shares issued under the 2015 Non-Executive Bonus Plan		5,638
Value of shares issued under the 2016 Bonus Plans	5,123
Value of shares issued under the Employee Stock Purchase Plan	$ 2,110	$ 2,579