Stockholders' Equity - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Equity [Abstract]
Cash Dividend on Common Stock	$ 0.55	$ 0.55	$ 0.55	$ 0.50	$ 1.65	$ 1.50
Aggregated Dividend Paid	$ 28.1	$ 28.0	$ 27.9
Common stock Dividend Payable Date	Oct. 15, 2014	Jul. 15, 2014	Apr. 14, 2014
Dividend payable date of record	Oct. 02, 2014	Jun. 27, 2014	Mar. 28, 2014
Dividend payable date declared	Sep. 19, 2014	May 06, 2014	Feb. 28, 2014
Company repurchased, shares						2.3
Repurchase agreement, Total cost						$ 100.0