Consolidated Statements of Changes in Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
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		5,173,000
Net (loss) income	21,667			21,667
Dividends paid	(21,737)			(21,737)
Change in fair value of marketable securities	(3,447)				(3,447)
Change in fair value of interest rate cap	56				56
Other	0		(6)			6
Ending Balance, Value at Mar. 31, 2017	349,384	$ 5,173	31,183	308,925	4,471	(368)
Ending Balance, Shares at Mar. 31, 2017		5,173,000
Beginning Balance, Value at Dec. 31, 2017	$ 343,955	$ 5,173	31,577	302,543	5,030	(368)
Beginning Balance, Shares at Dec. 31, 2017	5,173,450	5,173,000
Net (loss) income	$ (9,700)			(9,700)
Dividends paid	(23,022)			(23,022)
Cumulative effect of change in accounting principle (see Note 3)	0			5,156	(5,156)
Change in fair value of marketable securities	0
Change in fair value of interest rate cap	48				48
Ending Balance, Value at Mar. 31, 2018	$ 311,281	$ 5,173	$ 31,577	$ 274,977	$ (78)	$ (368)
Ending Balance, Shares at Mar. 31, 2018	5,173,450	5,173,000