Consolidated Statements of Changes in Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Capital	Retained   Earnings	Accumulated  Other Comprehensive (Loss) Income	Treasury Stock
Beginning Balance, Shares at Dec. 31, 2019		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 derivatives	7				7
Deferred stock unit grants	600		600
Ending Balance, Shares at Sep. 30, 2020		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 derivatives	(14)				(14)
Ending Balance, Shares at Sep. 30, 2020		5,173,000
Ending Balance, Value at Sep. 30, 2020	$ 208,511	$ 5,173	32,965	170,783	(42)	(368)
Beginning Balance, Shares at Dec. 31, 2020	5,173,450	5,173,000
Beginning Balance, Value at Dec. 31, 2020	$ 203,228	$ 5,173	32,965	166,165	(707)	(368)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	55,181			55,181
Dividends paid	(69,160)			(69,160)
Change in fair value of interest rate derivatives	4,612				4,612
Deferred stock unit grants	$ 450		450
Ending Balance, Shares at Sep. 30, 2021	5,173,450	5,173,000
Ending Balance, Value at Sep. 30, 2021	$ 194,311	$ 5,173	33,415	152,186	3,905	(368)
Beginning Balance, Shares at Jun. 30, 2021		5,173,000
Beginning Balance, Value at Jun. 30, 2021	205,805	$ 5,173	33,415	163,845	3,740	(368)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	11,401			11,401
Dividends paid	(23,060)			(23,060)
Change in fair value of interest rate derivatives	$ 165				165
Ending Balance, Shares at Sep. 30, 2021	5,173,450	5,173,000
Ending Balance, Value at Sep. 30, 2021	$ 194,311	$ 5,173	$ 33,415	$ 152,186	$ 3,905	$ (368)