Common and Preferred Stock - Additional Information (Detail) (USD $)	1 Months Ended	6 Months Ended
	Oct. 31, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Stockholders Equity Note [Line Items]
Increase in share repurchase authorized amount	$ 200,000,000
Purchase of common stock (in shares)		1,629,561
Purchase of common stock		84,479,000	36,042,000
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 outstanding
Repurchase Of Common Stock
Stockholders Equity Note [Line Items]
Purchase of common stock (in shares)		1,600,000	900,000
Purchase of common stock		86,700,000	36,000,000
July 2013 Settlement
Stockholders Equity Note [Line Items]
Purchase of common stock		$ 2,200,000