Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities:
Net loss	$ (9,238)	$ (16,492)	$ (31,238)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,159	1,663	2,213
Write-off of abandoned patents and licensed technology	230	350	889
Gain on sale of property and equipment	(1)	(15)	(7)
Compensation expense related to stock options and awards	1,902	3,159	3,466
Purchase of technology license with common stock	775	0	0
Changes in operating assets and liabilities:
Receivables and other assets	(178)	412	(2,626)
Accounts payable and accrued expenses	(1,415)	1,635	(2,188)
Deferred revenue	250	(150)	0
Deferred rent	(432)	(368)	(307)
Net cash used in operating activities	(6,948)	(9,806)	(29,798)
Cash flows from investing activities:
Maturities of marketable securities	20,183	10,556	30,974
Purchases of marketable securities	(20,114)	(22,643)	(5,137)
Purchases of property and equipment	(72)	(85)	(332)
Proceeds from the sale of property and equipment	3	15	49
Patent and licensed technology expenditures	(53)	(269)	(412)
Net cash (used in) provided by investing activities	(53)	(12,426)	25,142
Cash flows from financing activities:
Net proceeds from issuance of common stock	3	3,925	816
Payment of withholding taxes for net settlement of restricted stock units	(23)	(59)	(482)
Net cash (used in) provided by financing activities	(20)	3,866	334
Net decrease in cash and cash equivalents	(7,021)	(18,366)	(4,322)
Cash and cash equivalents at beginning of year	20,471	38,837	43,159
Cash and cash equivalents at end of year	$ 13,450	$ 20,471	$ 38,837