Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash flows from operating activities
Net income (loss)	$ (21,519)	$ 40,767
Adjustments to reconcile net income (loss) to net cash used in operating activities
Depreciation and amortization	864	628
Amortization of premium on marketable securities	1,356	876
Stock-based compensation	6,607	3,993
Abandonment of capitalized intangible assets	225	45
Gain on sale of marketable securities available-for-sale		(3)
Changes in operating assets and liabilities:
Accounts receivable	(6,260)	(150,310)
Interest receivable	(144)	160
Prepaid expenses and other assets	(4,727)	(1,031)
Accounts payable	3,500	1,294
Accrued expenses	(2,708)	(357)
Income taxes	390	1,781
Deferred rent	(12)	(53)
Deferred revenue	(1,080)	78,541
Net cash used in operating activities	(23,508)	(23,669)
Cash flows from investing activities
Purchase of marketable securities	(33,440)	(7,123)
Purchase of intangible assets	(1,092)	(761)
Purchase of property and equipment	(1,256)	(493)
Proceeds from sale and maturities of marketable securities	53,866	26,660
Net cash provided by investing activities	18,078	18,283
Cash flows from financing activities
Proceeds from issuance of common stock upon exercise of stock awards	1,680	447
Proceeds from issuance of common stock under the Employee Stock Purchase Plan	442	226
Net cash provided by financing activities	2,122	673
Net decrease in cash and cash equivalents	(3,308)	(4,713)
Cash and cash equivalents, beginning of period	14,528	12,590
Cash and cash equivalents, end of period	11,220	7,877
Cash paid during the period for:
Interest	5
Income taxes	60
Supplemental disclosures of non-cash investing activities
Unrealized gain on marketable securities available for sale	$ 201	$ 732