Condensed Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Voting Common Stock [Member] Common Stock [Member]	Voting Common Stock [Member]	Nonvoting Common Stock [Member] Common Stock [Member]	Nonvoting Common Stock [Member]	Paid-In Capital [Member]	Treasury Stock Voting [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Loss [Member]	Total
Balance at Dec. 31, 2019	$ 216		$ 95		$ 1,019,988	$ (9,592)	$ (605,766)	$ (54,914)	$ 350,027
Balance, shares at Dec. 31, 2019	21,582,000		9,506,000			154,000
Net income (loss)							(121,343)		(121,343)
Other comprehensive income (loss)								31,290	31,290
Comprehensive income (loss)									(90,053)
Balance at Mar. 31, 2020	$ 216		$ 95		1,019,988	$ (9,592)	(727,109)	(23,624)	259,974
Balance, shares at Mar. 31, 2020	21,582,000		9,506,000			154,000
Balance at Dec. 31, 2019	$ 216		$ 95		1,019,988	$ (9,592)	(605,766)	(54,914)	350,027
Balance, shares at Dec. 31, 2019	21,582,000		9,506,000			154,000
Other comprehensive income (loss)								(17,058)
Common dividends paid ($7.00 per share)									(216,500)
Balance at Dec. 31, 2020	$ 216		$ 95		1,019,988	$ (9,592)	(729,202)	(71,972)	209,533
Balance, shares at Dec. 31, 2020	21,582,000	21,581,572	9,506,000	9,505,673		154,000
Balance at Mar. 31, 2020	$ 216		$ 95		1,019,988	$ (9,592)	(727,109)	(23,624)	259,974
Balance, shares at Mar. 31, 2020	21,582,000		9,506,000			154,000
Net income (loss)							214,436
Other comprehensive income (loss)								(48,348)
Comprehensive income (loss)									166,088
Common dividends paid ($7.00 per share)							(216,529)		(216,529)
Balance at Dec. 31, 2020	$ 216		$ 95		1,019,988	$ (9,592)	(729,202)	(71,972)	209,533
Balance, shares at Dec. 31, 2020	21,582,000	21,581,572	9,506,000	9,505,673		154,000
Net income (loss)							30,716		30,716
Other comprehensive income (loss)								(1,816)	(1,816)
Comprehensive income (loss)									28,900
Balance at Mar. 31, 2021	$ 216		$ 95		$ 1,019,988	$ (9,592)	$ (698,486)	$ (73,788)	$ 238,433
Balance, shares at Mar. 31, 2021	21,582,000	21,581,572	9,506,000	9,505,673		154,000