Stockholders' Equity - Additional Information (Detail) - USD ($)	3 Months Ended				9 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Schedule Of Equity [Line Items]
Cash Dividend on Common Stock	$ 0.70	$ 0.65	$ 0.65	$ 0.55	$ 2.00	$ 1.65
Aggregated Dividend Paid	$ 35,900,000	$ 33,300,000	$ 33,300,000
Common stock Dividend Payable Date	Oct. 15, 2015	Jul. 15, 2015	Apr. 16, 2015
Dividend payable date of record	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015
Dividend payable date declared	Jul. 30, 2015	Jun. 09, 2015	Feb. 26, 2015
2015 Stock Repurchase Program [Member]
Schedule Of Equity [Line Items]
Authorized amount for share repurchase program	$ 100,000,000				$ 100,000,000
Company repurchased, shares	0				0