Earnings Per Share (EPS Calculation) (Details) - USD ($) $ / shares in Units, shares in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income	$ (2,062,000)	$ 40,198,000
Dividends	0	0
Undistributed earnings	(2,062,000)	40,198,000
Allocation of net income:
Dividends	0	0
Undistributed earnings	(2,062,000)	40,198,000
Net earnings	(2,062,000)	40,198,000
Class A
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income	(2,004,000)	39,061,000
Dividends	0	0
Undistributed earnings	(2,004,000)	39,061,000
Allocation of net income:
Dividends	0	0
Undistributed earnings	(2,004,000)	39,061,000
Net earnings	$ (2,004,000)	$ 39,061,000
Denominator:
Basic earnings (loss) per share - weighted-average shares (in shares)	3,436	3,436
Effect of dilutive stock options (in shares)	0	0
Diluted earnings (loss) per share - adjusted weighted-average shares for assumed conversions (in shares)	3,436	3,436
Basic earnings (loss) per share (in dollars per share)	$ (0.58)	$ 11.37
Diluted earnings (loss) per share (in dollars per share)	$ (0.58)	$ 11.37
Class B
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income	$ (58,000)	$ 1,137,000
Dividends	0	0
Undistributed earnings	(58,000)	1,137,000
Allocation of net income:
Dividends	0	0
Undistributed earnings	(58,000)	1,137,000
Net earnings	$ (58,000)	$ 1,137,000
Denominator:
Basic earnings (loss) per share - weighted-average shares (in shares)	200	200
Effect of dilutive stock options (in shares)	0	0
Diluted earnings (loss) per share - adjusted weighted-average shares for assumed conversions (in shares)	200	200
Basic earnings (loss) per share (in dollars per share)	$ (0.29)	$ 5.68
Diluted earnings (loss) per share (in dollars per share)	$ (0.29)	$ 5.68