Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Cash flows from operating activities
Net income (loss)	$ 40,767	$ (15,312)
Adjustments to reconcile net income (loss) to net cash used in operating activities
Depreciation and amortization	628	494
Amortization of premium on marketable securities	876	240
Stock-based compensation	3,993	2,300
Abandonment of capitalized intangible assets	45	54
Gain on disposal of assets		(9)
Gain on sale of marketable securities	(3)
Changes in operating assets and liabilities:
Accounts receivable	(150,310)	2,513
Interest receivable	160	(670)
Prepaid expenses and other assets	(1,031)	(538)
Accounts payable	1,294	1,387
Accrued expenses	(357)	328
Income taxes	1,781
Deferred rent	(53)	617
Deferred revenue	78,541	(413)
Net cash used in operating activities	(23,669)	(9,009)
Cash flows from investing activities
Purchase of marketable securities	(7,123)	(148,328)
Purchase of intangible assets	(761)	(915)
Purchase of property and equipment	(493)	(1,115)
Proceeds from sale and maturities marketable securities	26,660
Proceeds from sale of property and equipment		9
Net cash provided by (used in) investing activities	18,283	(150,349)
Cash flows from financing activities
Proceeds from issuance of common stock		122,906
Proceeds from issuance of common stock upon exercise of stock awards	447	429
Proceeds from issuance of common stock under the Employee Stock Purchase Plan	226	247
Common stock issuance cost		(7,702)
Net cash provided by financing activities	673	115,880
Net decrease in cash and cash equivalents	(4,713)	(43,478)
Cash and cash equivalents, beginning of period	12,590	12,590
Cash and cash equivalents, end of period	7,877	11,171
Supplemental disclosures of non-cash investing activities
Net unrealized gain (loss) on marketable securities, net of tax	$ 732	$ (90)