Consolidated Statements of Changes in Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock
Beginning Balance, Shares at Dec. 31, 2018		5,173,000
Beginning Balance, Value at Dec. 31, 2018	$ 285,092	$ 5,173	$ 31,971	$ 248,443	$ (127)	$ (368)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	29,148			29,148
Dividends paid	(46,056)			(46,056)
Change in fair value of interest rate cap	32				32
Deferred stock unit grants	394		394
Ending Balance, Shares at Jun. 30, 2019		5,173,000
Ending Balance, Value at Jun. 30, 2019	268,610	$ 5,173	32,365	231,535	(95)	(368)
Beginning Balance, Shares at Mar. 31, 2019		5,173,000
Beginning Balance, Value at Mar. 31, 2019	279,942	$ 5,173	31,971	243,280	(114)	(368)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	11,283			11,283
Dividends paid	(23,028)			(23,028)
Change in fair value of interest rate cap	19				19
Deferred stock unit grants	394		394
Ending Balance, Shares at Jun. 30, 2019		5,173,000
Ending Balance, Value at Jun. 30, 2019	$ 268,610	$ 5,173	32,365	231,535	(95)	(368)
Beginning Balance, Shares at Dec. 31, 2019	5,173,450	5,173,000
Beginning Balance, Value at Dec. 31, 2019	$ 253,515	$ 5,173	32,365	216,394	(49)	(368)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	16,903			16,903
Dividends paid	(46,068)			(46,068)
Change in fair value of interest rate cap	21				21
Deferred stock unit grants	$ 600		600
Ending Balance, Shares at Jun. 30, 2020	5,173,450	5,173,000
Ending Balance, Value at Jun. 30, 2020	$ 224,971	$ 5,173	32,965	187,229	(28)	(368)
Beginning Balance, Shares at Mar. 31, 2020		5,173,000
Beginning Balance, Value at Mar. 31, 2020	235,078	$ 5,173	32,365	197,932	(24)	(368)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	12,331			12,331
Dividends paid	(23,034)			(23,034)
Change in fair value of interest rate cap	(4)				(4)
Deferred stock unit grants	$ 600		600
Ending Balance, Shares at Jun. 30, 2020	5,173,450	5,173,000
Ending Balance, Value at Jun. 30, 2020	$ 224,971	$ 5,173	$ 32,965	$ 187,229	$ (28)	$ (368)