Stockholders' Equity - Dividend Activity (Details) - USD ($)													12 Months Ended
	Nov. 24, 2017	Aug. 31, 2017	May 19, 2017	Mar. 03, 2017	Nov. 25, 2016	Aug. 26, 2016	May 20, 2016	Mar. 24, 2016	Nov. 20, 2015	Aug. 28, 2015	May 29, 2015	Mar. 27, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stockholders' Equity Note [Abstract]
Dividends Per Share, Common (in dollars per share)	$ 0.12	$ 0.11	$ 0.10	$ 0.09	$ 0.08	$ 0.07	$ 0.06	$ 0.05	$ 0.05	$ 0.04	$ 0.03	$ 0.02	$ 1.52	$ 0.61	$ 0.14
CommonStockSpecialDividendsPerShareDeclared	$ 0.15	$ 0.25	$ 0.35	$ 0.35	$ 0.35
Dividends, cash	$ 1,360,000	$ 1,246,000	$ 1,133,000	$ 1,019,000	$ 901,000	$ 787,000	$ 686,000	$ 576,000	$ 598,000	$ 489,000	$ 372,000	$ 250,000	$ 17,218,000	$ 6,891,000	$ 1,709,000
Payment Date	Nov. 24, 2017	Aug. 31, 2017	May 19, 2017	Mar. 03, 2017	Nov. 25, 2016	Aug. 26, 2016	May 20, 2016	Mar. 24, 2016	Nov. 20, 2015	Aug. 28, 2015	May 29, 2015	Mar. 27, 2015
Dividends, Common Stock, Cash	$ 1,701,000	$ 2,833,000	$ 3,964,000	$ 3,962,000	$ 3,941,000