Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Capital	Retained Earnings	Accumulated Other Comprehensive Income	Treasury Stock
Opening Balance, at Dec. 31, 2014	$ 348,399	$ 5,173	$ 30,139	$ 299,004	$ 14,457	$ (374)
Opening Balance (in shares) at Dec. 31, 2014		5,173,000
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 grant	600		600
Closing Balance (in shares) at Sep. 30, 2015		5,173,000
Closing Balance, at Sep. 30, 2015	345,124	$ 5,173	30,739	298,664	10,922	(374)
Opening Balance, at Dec. 31, 2015	$ 352,880	$ 5,173	30,739	304,340	13,002	(374)
Opening Balance (in shares) at Dec. 31, 2015	5,173,450	5,173,000
Net income	$ 64,822			64,822
Dividends paid	(61,363)			(61,363)
Change in unrealized net gain on available-for-sale securities	96				96
Change in value of interest rate cap	80				80
Deferred stock unit grant	$ 450		450
Closing Balance (in shares) at Sep. 30, 2016	5,173,450	5,173,000
Closing Balance, at Sep. 30, 2016	$ 356,965	$ 5,173	$ 31,189	$ 307,799	$ 13,178	$ (374)