Stockholders' Equity - Additional Information (Detail) - USD ($)	1 Months Ended		3 Months Ended						9 Months Ended
	Oct. 31, 2016	May 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Sep. 30, 2016	Sep. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend declared and paid per share			$ 0.18	$ 0.18	$ 0.18	$ 0.17	$ 0.17	$ 0.17
Aggregate dividend declared for the year									$ 9,700,000	$ 9,200,000
Dividend declared per share			$ 0.18			$ 0.17			$ 0.54	$ 0.51
Authorized to purchase of common stock under the stock repurchase program			$ 460,000,000						$ 460,000,000
Repurchase of common Stock						200,000			0	500,000
Cumulative aggregate cost of repurchase of common stock						$ 6,900,000				$ 18,600,000
Cumulative repurchase of common stock			15,000,000						15,000,000
Aggregate cost of repurchase of common stock									$ 423,100,000
Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend declared per share	$ 0.18
Dividend payable, date declared	Dec. 21, 2016
Dividend payable, record date	Dec. 07, 2016
Increase in authorized to purchase of common stock under the stock repurchase program	$ 25,000,000
2006 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity incentive plan extended term		10 years
Equity incentive plan expiration		2026-05
Increase in number of shares issuable under plan		2,000,000