Quarterly Financial Data (Detail) (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
Quarterly Financial Data [Line Items]
Revenues	$ 8,495	$ 16,759	$ 20,884	$ 20,587	$ 20,455	$ 20,791	$ 20,614	$ 20,897	$ 66,725	$ 82,757	$ 100,041
Operating expenses	96,844	34,906	32,951	31,480	34,041	33,229	33,732	36,573	196,181	137,575	144,111
Net loss	$ (62,188)	$ (19,502)	$ (12,956)	$ (11,368)	$ (14,303)	$ (13,237)	$ (13,824)	$ (16,285)	$ (106,014)	$ (57,649)	$ (43,515)
Net loss per common share - basic and diluted	$ (1.20)	$ (0.38)	$ (0.25)	$ (0.25)	$ (0.33)	$ (0.31)	$ (0.33)	$ (0.38)	$ (2.11)	$ (1.36)	$ (1.04)
Weighted average common shares - basic and diluted	51,821	51,542	51,280	46,210	42,715	42,654	42,379	42,345	50,286	42,410	42,040