Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Cash flows from operating activities:
Net loss	$ (29,046)	$ (15,350)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,731	1,691
Write-off of abandoned patents and licensed technology	778	71
Gain on sale of property and equipment		(9)
Compensation expense related to stock options and awards	2,686	2,578
Changes in operating assets and liabilities:
Receivables and other assets	323	593
Accounts payable and accrued expenses	(502)	(816)
Deferred revenue	(113)	(99)
Deferred rent	(220)	(176)
Net cash used in operating activities	(24,363)	(11,517)
Cash flows from investing activities:
Proceeds from the sale of marketable securities		3,750
Maturities of marketable securities	25,489	13,741
Purchases of marketable securities	(5,137)	(39,412)
Purchases of property and equipment	(307)	(529)
Proceeds from the sale of property and equipment	1	9
Patent expenditures	(376)	(318)
Net cash provided by (used in) investing activities	19,670	(22,759)
Cash flows from financing activities:
Net proceeds from issuance of common stock	815	48,931
Payment of withholding taxes for net settlement of restricted stock units	(470)	(201)
Net cash provided by financing activities	345	48,730
Net (decrease) increase in cash and cash equivalents	(4,348)	14,454
Cash and cash equivalents at beginning of period	43,159	38,696
Cash and cash equivalents at end of period	$ 38,811	$ 53,150