Treasury Stock - Additional Information (Detail) (USD $)	1 Months Ended		9 Months Ended
	Sep. 30, 2012	Aug. 05, 2011	Sep. 30, 2012	Sep. 30, 2011
Equity, Class of Treasury Stock [Line Items]
Authorization to repurchase common stock		$ 300,000,000
Share repurchase end date		Dec. 31, 2014
Repurchase of common stock, shares			799,533
Repurchase of common stock, average cost per share			$ 42.35
Repurchase of common stock, value			33,863,000	15,797,000
Stock repurchase program, amount available for the repurchase of our common stock	$ 250,300,000
Treasury shares issued			132,846
Issuance of treasury shares, average cost per share			$ 6.63
Shares repurchased to satisfy employee withholding tax requirements resulting from certain restricted stock units becoming vested			43,874
Common stock repurchased, average cost			$ 42.64
Shares held in treasury	18,346,468		18,346,468