Stockholders' Equity and Warrants - Additional Information (Detail) (USD $)	1 Months Ended			3 Months Ended	12 Months Ended			1 Months Ended
	Dec. 20, 2011	Oct. 29, 2010	Feb. 25, 2009	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Jan. 29, 2013 Subsequent Event	Dec. 20, 2011 Common stock	Oct. 29, 2010 Common stock	Feb. 25, 2009 Common stock	Jan. 29, 2013 Common stock Subsequent Event
Stockholders Equity Note [Line Items]
Preferred stock, authorized					10,000,000	10,000,000
Common stock, authorized					240,000,000	240,000,000
Shares of common stock sold									24,725,000	16,000,000	14,378,698	16,489,893
Common stock purchase price	$ 10.42	$ 3.70	$ 1.69					$ 19.60
Net proceed from sale of common stock	$ 243,100,000	$ 57,500,000	$ 22,800,000			$ 243,058,000	$ 57,515,000	$ 309,800,000
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				12,483,000	12,483,000	8,080,000	2,624,000
Adjustment of additional paid-up capital up on exercise of warrants					$ 87,000,000