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	45,641			45,641
Dividends paid	(69,090)			(69,090)
Change in fair value of interest rate cap	54				54
Deferred stock unit grants	394		394
Ending Balance, Shares at Sep. 30, 2019		5,173,000
Ending Balance, Value at Sep. 30, 2019	262,091	$ 5,173	32,365	224,994	(73)	(368)
Beginning Balance, Shares at Jun. 30, 2019		5,173,000
Beginning Balance, Value at Jun. 30, 2019	268,610	$ 5,173	32,365	231,535	(95)	(368)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	16,493			16,493
Dividends paid	(23,034)			(23,034)
Change in fair value of interest rate cap	22				22
Ending Balance, Shares at Sep. 30, 2019		5,173,000
Ending Balance, Value at Sep. 30, 2019	$ 262,091	$ 5,173	32,365	224,994	(73)	(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	23,507			23,507
Dividends paid	(69,118)			(69,118)
Change in fair value of interest rate cap	7				7
Deferred stock unit grants	$ 600		600
Ending Balance, Shares at Sep. 30, 2020	5,173,450	5,173,000
Ending Balance, Value at Sep. 30, 2020	$ 208,511	$ 5,173	32,965	170,783	(42)	(368)
Beginning Balance, Shares at Jun. 30, 2020		5,173,000
Beginning Balance, Value at Jun. 30, 2020	224,971	$ 5,173	32,965	187,229	(28)	(368)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	6,604			6,604
Dividends paid	(23,050)			(23,050)
Change in fair value of interest rate cap	$ (14)				(14)
Ending Balance, Shares at Sep. 30, 2020	5,173,450	5,173,000
Ending Balance, Value at Sep. 30, 2020	$ 208,511	$ 5,173	$ 32,965	$ 170,783	$ (42)	$ (368)