Stockholders' Equity and Warrants - Additional Information (Detail) (USD $)	1 Months Ended		3 Months Ended	6 Months Ended		12 Months Ended
	Jan. 29, 2013	Feb. 25, 2009	Mar. 31, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2011	Jun. 20, 2013	Dec. 31, 2012
Stockholders Equity Note [Line Items]
Common stock, authorized				450,000,000			240,000,000	240,000,000
Common stock purchase price	$ 19.60	$ 1.69
Net proceed from sale of common stock	$ 310,000,000	$ 22,800,000		$ 310,037,000
Warrants issued		10,784,024
Exercise price of warrants		2.15
Warrants exercised			5,805,843			4,978,181
Proceeds from warrants exercised			12,500,000		12,482,000	10,700,000
Adjustment of additional paid-up capital up on exercise of warrants			$ 87,000,000
Common stock
Stockholders Equity Note [Line Items]
Shares of common stock sold	16,489,893	14,378,698