Stockholders' Equity - Additional Information (Detail) - USD ($)	1 Months Ended		3 Months Ended												12 Months Ended
	Jan. 31, 2016	Jan. 31, 2014	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Oct. 31, 2016	Jul. 31, 2014
Class of Stock [Line Items]
Common stock, shares authorized			110,000,000				110,000,000								110,000,000	110,000,000
Common stock entitles															One
Shares repurchase program authorized	$ 25,000,000	$ 35,000,000																	$ 65,000,000
Amount available for repurchase			$ 51,100,000												$ 51,100,000
Cash dividends declared per common share			$ 0.26	$ 0.26	$ 0.26	$ 0.26	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.16	$ 0.16	$ 0.16	$ 0.16	$ 1.04	$ 0.80	$ 0.64
Share Repurchase Program [Member]
Class of Stock [Line Items]
Shares repurchase program period		2 years
Total shares repurchased		917,354
New Share Repurchase Program [Member]
Class of Stock [Line Items]
Shares repurchase program period	2 years
Total shares repurchased	155,868
Commencement date															Mar. 01, 2016
Shares repurchase program additional authorized amount																		$ 50,000,000
Common Stock Non-Voting [Member]
Class of Stock [Line Items]
Common stock, shares authorized			10,000,000				10,000,000								10,000,000	10,000,000
Common Stock Voting [Member]
Class of Stock [Line Items]
Common stock, shares authorized			110,000,000				110,000,000								110,000,000	110,000,000