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	32,072			32,072
Dividends paid	(33,213)			(33,213)
Change in unrealized net gain on available-for-sale securities	4,207				4,207
Change in value of interest rate cap	(153)				(153)
Deferred stock unit grant	394		394
Shares Issued, Ending Balance (in shares) at Jun. 30, 2014		5,173,000
Balance, at Jun. 30, 2014	$ 336,888	$ 5,173	30,139	296,374	5,576	(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	35,163			35,163
Dividends paid	(35,780)			(35,780)
Change in unrealized net gain on available-for-sale securities	(4,715)				(4,715)
Change in value of interest rate cap	(10)				(10)
Deferred stock unit grant	$ 600		600
Shares Issued, Ending Balance (in shares) at Jun. 30, 2015	5,173,450	5,173,000
Balance, at Jun. 30, 2015	$ 343,657	$ 5,173	$ 30,739	$ 298,387	$ 9,732	$ (374)