Stockholders' Equity (Details) - USD ($)	3 Months Ended						9 Months Ended		12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Changes in the components of stockholders' equity
Balance at the beginning of the period			$ 63,968,000				$ 63,968,000
Net earnings (loss)	$ 13,190,000			$ (414,000)			9,361,000	$ 2,597,000
Change in net actuarial loss and prior service cost, net of income tax expense	29,000			29,000			87,000	80,000
Balance at the end of the period	73,578,000						73,578,000		$ 63,968,000
Income tax expense on change in net actuarial loss and prior service cost	12,000	$ 12,000	11,000	10,000	$ 10,000	$ 10,000
Accumulated other comprehensive loss, net of income taxes
Net actuarial loss and prior service cost not yet recognized in net periodic benefit cost, net of income tax benefit	3,604,000			3,278,000			3,604,000	3,278,000	3,691,000	$ 3,358,000
Income tax benefit on net actuarial loss and prior service cost not yet recognized in net periodic benefit cost							2,450,000	2,319,000	2,485,000	2,350,000
Common Stock | Common Stock
Changes in the components of stockholders' equity
Balance at the beginning of the period	1,788,000	1,790,000	1,782,000	1,809,000	1,809,000	1,805,000	1,782,000	1,805,000	1,805,000
Issuance of restricted stock awards, net of forfeitures	(2,000)	(2,000)	13,000			14,000
Repurchase and retirement of common stock			(5,000)	(16,000)		(10,000)
Balance at the end of the period	1,786,000	1,788,000	1,790,000	1,793,000	1,809,000	1,809,000	1,786,000	1,793,000	1,782,000	1,805,000
Common Stock | Class A Common Stock
Changes in the components of stockholders' equity
Balance at the beginning of the period	1,851,000	1,851,000	1,851,000	1,851,000	1,851,000	1,851,000	1,851,000	1,851,000	1,851,000
Balance at the end of the period	1,851,000	1,851,000	1,851,000	1,851,000	1,851,000	1,851,000	1,851,000	1,851,000	1,851,000	1,851,000
Additional Paid-in Capital
Changes in the components of stockholders' equity
Balance at the beginning of the period	101,112,000	100,984,000	100,994,000	101,388,000	101,320,000	101,416,000	100,994,000	101,416,000	101,416,000
Issuance of restricted stock awards, net of forfeitures	2,000	2,000	(13,000)			(14,000)
Stock-based compensation	38,000	126,000	92,000	67,000	68,000	108,000
Repurchase and retirement of common stock			(89,000)	(312,000)		(190,000)
Balance at the end of the period	101,152,000	101,112,000	100,984,000	101,143,000	101,388,000	101,320,000	101,152,000	101,143,000	100,994,000	101,416,000
Accumulated Deficit
Changes in the components of stockholders' equity
Balance at the beginning of the period	(40,797,000)	(40,108,000)	(36,968,000)	(35,815,000)	(41,316,000)	(38,826,000)	(36,968,000)	(38,826,000)	(38,826,000)
Net earnings (loss)	13,190,000	(689,000)	(3,140,000)	(414,000)	5,501,000	(2,490,000)
Balance at the end of the period	(27,607,000)	(40,797,000)	(40,108,000)	(36,229,000)	(35,815,000)	(41,316,000)	(27,607,000)	(36,229,000)	(36,968,000)	(38,826,000)
Accumulated Other Comprehensive Loss
Changes in the components of stockholders' equity
Balance at the beginning of the period	(3,633,000)	(3,662,000)	(3,691,000)	(3,307,000)	(3,333,000)	(3,358,000)	(3,691,000)	(3,358,000)	(3,358,000)
Change in net actuarial loss and prior service cost, net of income tax expense	29,000	29,000	(29,000)	29,000	26,000	25,000
Balance at the end of the period	$ (3,604,000)	$ (3,633,000)	$ (3,662,000)	$ (3,278,000)	$ (3,307,000)	$ (3,333,000)	$ (3,604,000)	$ (3,278,000)	$ (3,691,000)	$ (3,358,000)