Common and Preferred Stock - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended
	Oct. 31, 2012	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Stockholders Equity Note [Line Items]
Increase in share repurchase authorized amount	$ 200,000,000
Purchase of common stock (in shares)		706,491
Purchase of common stock		33,115,000	10,183,000
Common stock, shares authorized		150,000,000		150,000,000
Common stock, par value		$ 0.01		$ 0.01
Preferred stock, shares authorized		5,000,000		5,000,000
Preferred stock, par value		$ 0.01		$ 0.01
Preferred stock, shares issued
Repurchase Of Common Stock
Stockholders Equity Note [Line Items]
Purchase of common stock (in shares)		706,491	200,000
Purchase of common stock		35,700,000	10,183,000
April Settlement
Stockholders Equity Note [Line Items]
Purchase of common stock		$ 2,600,000