Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Beginning Balance, Value at Dec. 31, 2015	$ 352,880	$ 5,173	$ 30,739	$ 304,340	$ 13,002	$ (374)
Beginning Balance, Shares at Dec. 31, 2015		5,173,000
Net income	64,822			64,822
Dividends paid	(61,363)			(61,363)
Change in unrealized net gain or loss on available-for-sale securities	96				96
Change in value of interest rate cap	80				80
Deferred stock unit grants	450		450
Ending Balance, Value at Sep. 30, 2016	356,965	$ 5,173	31,189	307,799	13,178	(374)
Ending Balance, Shares at Sep. 30, 2016		5,173,000
Beginning Balance, Value at Dec. 31, 2016	$ 352,845	$ 5,173	31,189	308,995	7,862	(374)
Beginning Balance, Shares at Dec. 31, 2016	5,173,450	5,173,000
Net income	$ 62,626			62,626
Dividends paid	(65,218)			(65,218)
Change in unrealized net gain or loss on available-for-sale securities	(8,494)				(8,494)
Change in value of interest rate cap	(67)				(67)
Deferred stock unit grants	394		394
Other	0		(6)			6
Ending Balance, Value at Sep. 30, 2017	$ 342,086	$ 5,173	$ 31,577	$ 306,403	$ (699)	$ (368)
Ending Balance, Shares at Sep. 30, 2017	5,173,450	5,173,000