Stockholders' Equity and Warrants - Additional Information (Detail) (USD $)	1 Months Ended		3 Months Ended	9 Months Ended		12 Months Ended
	Dec. 20, 2011	Feb. 25, 2009	Mar. 31, 2012	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Dec. 31, 2010	Jan. 11, 2010
Stockholders Equity Note [Line Items]
Common stock, authorized				240,000,000		240,000,000
Common stock purchase price	$ 10.42	$ 1.69
Net proceed from sale of common stock	$ 243,100,000	$ 22,800,000
Warrants issued		10,784,024
Exercise price of warrants		2.15
Warrants exercised			5,805,843			3,757,767	1,220,414
Proceeds from warrants exercised			12,500,000	12,482,000	8,079,000	8,100,000	2,600,000
Adjustment of additional paid-up capital up on exercise of warrants			87,000,000
Shelf registration statement, total value								125,000,000
Shelf registration statement, remaining value				$ 65,800,000
Common stock
Stockholders Equity Note [Line Items]
Shares of common stock sold	24,725,000	14,378,698