Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions	1 Months Ended	3 Months Ended				6 Months Ended
	Jul. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2014	Mar. 31, 2014	Jun. 30, 2015	Jun. 30, 2014	Feb. 28, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend paid per share		$ 0.17	$ 0.17	$ 0.16	$ 0.16
Aggregate dividend declared for the year						$ 6,100,000	$ 6,100,000
Cash dividends declared per common share		$ 0.17		$ 0.16		$ 0.34	$ 0.32
Increase in authorized to purchase of common stock under the stock repurchase program								$ 25,000,000
Authorized to purchase of common stock under the stock repurchase program		$ 435,000,000				$ 435,000,000
Repurchase of common Stock		0.2		0.7		0.3	1.5
Cumulative aggregate cost of repurchase of common stock		$ 6,100,000		$ 25,200,000		$ 11,800,000	$ 54,900,000
Cumulative repurchase of common stock		14.7				14.7
Aggregate cost of repurchase of common stock						$ 414,000,000
Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cash dividends declared per common share	$ 0.17
Dividend payable date	Sep. 16, 2015
Dividend payable record date	Sep. 02, 2015
Increase in authorized to purchase of common stock under the stock repurchase program	$ 25,000,000