CONDENSED STATEMENTS OF CASH FLOWS (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Cash flows from operating activities:
Net loss	$ (5,775)	$ (4,260)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	235	281
Amortization of premium/discount on marketable securities	625	200
Amortization of deferred gain on sale leaseback	(140)	(140)
Non-cash stock compensation	1,365	1,198
Loss (gain) on auction rate securities	2	(85)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(481)	2,448
Other assets	81	(31)
Accounts payable and accrued expenses	(2,681)	(286)
Deferred revenue	(3,571)	(8,345)
Net cash used in operating activities	(10,340)	(9,020)
Cash flows from investing activities:
Purchases of marketable securities	(616)	(14,307)
Proceeds from sale or maturity of marketable securities	11,603	30,934
Purchases of property and equipment		(73)
Net cash provided by investing activities	10,987	16,554
Cash flows from financing activities:
Proceeds from stock option exercises		904
Net cash provided by financing activities		904
Net increase in cash and cash equivalents	647	8,438
Cash and cash equivalents, beginning of period	14,327	11,095
Cash and cash equivalents, end of period	$ 14,974	$ 19,533