Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net loss	$ (16,492)	$ (31,238)	$ (22,899)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,663	2,213	2,328
Write-off of abandoned patents and licensed technology	350	889	71
Gain on sale of property and equipment	(15)	(7)	(9)
Compensation expense related to stock options and awards	3,159	3,466	3,290
Changes in operating assets and liabilities:
Receivables and other assets	412	(2,626)	977
Accounts payable and accrued expenses	1,635	(2,188)	(792)
Deferred revenue	(150)	0	51
Deferred rent	(368)	(307)	(247)
Net cash used in operating activities	(9,806)	(29,798)	(17,230)
Cash flows from investing activities:
Proceeds from the sale of marketable securities	0	0	3,750
Maturities of marketable securities	10,556	30,974	22,151
Purchases of marketable securities	(22,643)	(5,137)	(51,842)
Purchases of property and equipment	(85)	(332)	(646)
Proceeds from the sale of property and equipment	15	49	9
Patent and licensed technology expenditures	(269)	(412)	(409)
Net cash (used in) provided by investing activities	(12,426)	25,142	(26,987)
Cash flows from financing activities:
Net proceeds from issuance of common stock	3,925	816	48,933
Payment of withholding taxes for net settlement of restricted stock units	(59)	(482)	(253)
Net cash provided by financing activities	3,866	334	48,680
Net (decrease) increase in cash and cash equivalents	(18,366)	(4,322)	4,463
Cash and cash equivalents at beginning of year	38,837	43,159	38,696
Cash and cash equivalents at end of year	$ 20,471	$ 38,837	$ 43,159