Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Capital	Retained Earnings	Accumulated Other Comprehensive Income	Treasury Stock
Shares Issued, Beginning Balance (in shares) at Dec. 31, 2013		5,173,000
Balance, at Dec. 31, 2013	$ 333,581	$ 5,173	$ 29,745	$ 297,515	$ 1,522	$ (374)
Net income	49,764			49,764
Dividends paid	(49,825)			(49,825)
Change in unrealized net gain on available-for-sale securities	2,644				2,644
Change in value of interest rate cap	(183)				(183)
Deferred stock unit grants	394		394
Shares Issued, Ending Balance (in shares) at Sep. 30, 2014		5,173,000
Balance, at Sep. 30, 2014	$ 336,375	$ 5,173	30,139	297,454	3,983	(374)
Shares Issued, Beginning Balance (in shares) at Dec. 31, 2014	5,173,450	5,173,000
Balance, at Dec. 31, 2014	$ 348,399	$ 5,173	30,139	299,004	14,457	(374)
Net income	53,335			53,335
Dividends paid	(53,675)			(53,675)
Change in unrealized net gain on available-for-sale securities	(3,527)				(3,527)
Change in value of interest rate cap	(8)				(8)
Deferred stock unit grants	$ 600		600
Shares Issued, Ending Balance (in shares) at Sep. 30, 2015	5,173,450	5,173,000
Balance, at Sep. 30, 2015	$ 345,124	$ 5,173	$ 30,739	$ 298,664	$ 10,922	$ (374)