Stockholders Equity and Warrants- Narrative (Detail) (USD $)	1 Months Ended				12 Months Ended
	Dec. 31, 2011	Oct. 31, 2010	Aug. 31, 2009	Feb. 28, 2009 Right	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Oct. 29, 2011	Jan. 21, 2010
Stockholders Equity Note [Line Items]
Preferred stock, authorized	10,000,000				10,000,000	10,000,000
Common stock, authorized	240,000,000				240,000,000	240,000,000
Issuance of common stock, net of issuance costs (in shares)	24,725,000	16,000,000	21,850,000	14,378,698
Shares of common stock issued upon exercise by the underwriters of their over-allotment option			2,850,000
Common stock issuance price	$ 10.42	$ 3.7	$ 1.75	$ 1.69	$ 10.42
Issuance of common stock, net of issuance costs	$ 243,058,000	$ 57,515,000	$ 35,600,000	$ 22,800,000	$ 243,058,000	$ 57,515,000	$ 58,370,000
Warrants issued				10,784,024
Exercise price of warrants				2.15
Issuance of common stock from warrant exercise					3,757,767	1,220,414
Warrants exercise date				Aug. 25, 2009
Warrants expiration date				2012-02-25
Proceeds from issuance of common stock pursuant to warrants					8,080,000	2,624,000
Adjustment of additional paid-up capital up on exercise of warrants					25,000,000	4,700,000
Warrants outstanding, rights	5,805,843				5,805,843
Warrants outstanding, value	12,500,000				12,500,000
Shelf registration statement, total value									125,000,000
Shelf registration statement, remaining value								$ 65,800,000