CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
CASH FLOWS FROM OPERATING ACTIVITIES
Net (loss) income	$ (1,387)	$ 4,858
Adjustments to reconcile net (loss) income to net cash used in operating activities:
Depreciation and amortization	318	414
Gain on sale of assets	(1,542)	(1,571)
Cease-use expense		176
Deferred revenues	(18,266)	(18,550)
Deferred rent	159	215
Amortization of premiums on investments	1,490	1,153
Non-cash share-based compensation expense	2,799	1,107
Change in operating assets and liabilities:
Receivables under collaboration agreements and other assets	(345)	1,308
Accounts payable and accrued liabilities	(1,205)	(1,167)
Cease-use liability	(129)	(2,433)
Other liabilities	26
Net cash used in operating activities	(18,082)	(14,490)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchases of investments	(123,161)	(75,879)
Sales and maturities of investments	50,455	54,986
Deposits and restricted cash	(28)	(2)
Proceeds from sales of property and equipment	25	101
Purchases of property and equipment	(594)	(148)
Net cash used in investing activities	(73,303)	(20,942)
CASH FLOWS FROM FINANCING ACTIVITIES
Issuance of common stock	83,296	219
Net cash provided by financing activities	83,296	219
Net decrease in cash and cash equivalents	(8,089)	(35,213)
Cash and cash equivalents at beginning of the period	50,107	54,051
Cash and cash equivalents at end of the period	$ 42,018	$ 18,838