Common Stock (Details) - $ / shares					3 Months Ended								12 Months Ended
	Jan. 29, 2016	Jan. 04, 2016	Sep. 25, 2014	Sep. 24, 2014	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, 2015	Dec. 31, 2014	Dec. 31, 2013	Aug. 06, 2015
Class of Stock [Line Items]
Authorized shares to be repurchased																1,000,000
Dividends declared (in dollars per share)					$ 0.08	$ 0.08	$ 0.08	$ 0.08	$ 0.07	$ 0.07	$ 0.07	$ 0.07
Dividends paid (in dollars per share)													$ 0.32	$ 0.28	$ 0.28
Subsequent Event
Class of Stock [Line Items]
Dividends declared (in dollars per share)		$ 0.09
Dividends paid (in dollars per share)	$ 0.09
Share Repurchase Agreement with Capital Southwest Corporation and Capital Southwest Venture Corporation
Class of Stock [Line Items]
Authorized shares to be repurchased				849,690
Purchase price per share				$ 40.255
Share Price (in dollars per share)				$ 41.50
Retirement of shares (shares)			849,690