Treasury Stock - Additional Information (Detail) (USD $)	1 Months Ended	6 Months Ended
	Aug. 05, 2011	Jun. 30, 2012
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		510,878
Repurchase of common stock, average cost per share		$ 43.23
Repurchase of common stock, value		$ 22,086,000
Treasury shares issued		120,446
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		39,510
Common stock repurchased, average cost		$ 42.83
Shares held in treasury		18,065,849