Summary of Unaudited Quarterly Financial Information (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Summary of the Company's unaudited quarterly results of operations
Total revenues	$ 2,319	$ 2,175	$ 1,565	$ 11,460	$ 1,932	$ 26,619	$ 818	$ 649	$ 17,519	$ 30,018	$ 8,711
Total operating expenses	9,895	9,955	9,502	11,600	8,978	10,227	9,269	9,366	40,952	37,840	39,926
Net income (loss)	$ (7,549)	$ (7,726)	$ (7,868)	$ 244	$ (6,614)	$ 16,431	$ (8,406)	$ (8,694)	$ (22,899)	$ (7,283)	$ (30,385)
Basic net income (loss) per share (1)	$ (0.09)	$ (0.09)	$ (0.09)	$ 0.00	$ (0.09)	$ 0.23	$ (0.12)	$ (0.12)
Diluted net income (loss) per share (1)	$ (0.09)	$ (0.09)	$ (0.09)	$ 0.00	$ (0.09)	$ 0.22	$ (0.12)	$ (0.12)