Stockholders' Equity and Warrants - Additional Information (Detail) (USD $)	1 Months Ended		3 Months Ended		12 Months Ended		1 Months Ended
	Dec. 20, 2011	Feb. 25, 2009	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011	Dec. 31, 2010	Dec. 20, 2011 Common Stock	Feb. 25, 2009 Common Stock	Jan. 11, 2010 Maximum
Stockholders Equity Note [Line Items]
Common stock, authorized			240,000,000		240,000,000
Shares of common stock sold							24,725,000	14,378,698
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			12,482,000	7,580,000	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