Treasury Stock - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended	9 Months Ended
	Aug. 05, 2011	Sep. 30, 2011	Sep. 30, 2011
Equity, Class of Treasury Stock [Line Items]
Treasury shares issued			370,071
Authorization to repurchase common stock	$ 300,000,000
Issuance of treasury shares, average cost per share			$ 6.63
Repurchase of common stock, shares		441,416
Repurchase of common stock, shares			140,233
Repurchase of common stock, average cost per share		$ 35.79	$ 36.57
Shares held in treasury		17,638,060	17,638,060
Repurchase of common stock, Value		$ 15,800,000	$ 15,797,000