Common and Preferred Stock - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	0 Months Ended	12 Months Ended
	Nov. 06, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Equity [Abstract]
Increase in share repurchase authorized amount	$ 400.0
Purchase of common stock (in shares)		2,970,461	2,916,280	2,182,946
Purchase of common stock		222.5	167.5
Remaining authorized repurchase amount			$ 545
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		0	0