Treasury Stock - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended
	Aug. 05, 2011	Mar. 31, 2012
Equity, Class of Treasury Stock [Line Items]
Authorization to repurchase common stock	$ 300,000,000
Repurchase of common stock, shares		114,199
Repurchase of common stock, average cost per share		$ 43.92
Repurchase of common stock, Value		$ 5,015,000
Treasury shares issued		113,720
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		17,675,896