Stockholders' Equity (Details)		12 Months Ended
	Jun. 14, 2016	Dec. 31, 2020 USD ($) Vote $ / shares	Dec. 31, 2019 USD ($) $ / shares	Dec. 31, 2018 USD ($) $ / shares	Jan. 01, 2018 USD ($)
Changes in the components of stockholders' equity
Balance at the beginning of the period		$ 63,968,000
Net earnings		7,482,000	$ 5,500,000	$ 6,889,000
Dividends paid		2,546,000	3,642,000	2,930,000
Change in net actuarial loss and prior service cost, net of income tax expense		(94,000)	(333,000)	155,000
Balance at the end of the period		69,027,000	63,968,000
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		(3,785,000)	(3,691,000)
Income tax benefit on net actuarial loss and prior service cost not yet recognized in net periodic benefit cost		$ 2,521,000	2,485,000
Minimum percentage of common stock to be acquired for rights to detach and be traded separately from common stock	10.00%
Minimum percentage of common stock to be announced for tender or exchange for rights to detach and be traded separately from common stock	10.00%
Common Class A [Member]
Changes in the components of stockholders' equity
Number of votes per share | Vote		10
Common Stock [Member]
Changes in the components of stockholders' equity
Balance at the beginning of the period		$ 1,782,000	1,805,000	1,825,000
Issuance of restricted stock awards, net of forfeitures		9,000	14,000	15,000
Repurchase and retirement of common stock		(5,000)	(37,000)	(35,000)
Balance at the end of the period		$ 1,786,000	1,782,000	1,805,000
Number of votes per share | Vote		1
Common Stock [Member] | Common Class A [Member]
Changes in the components of stockholders' equity
Balance at the beginning of the period		$ 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
Additional Paid-in Capital [Member]
Changes in the components of stockholders' equity
Balance at the beginning of the period		100,994,000	101,416,000	101,844,000
Issuance of restricted stock awards, net of forfeitures		(9,000)	(14,000)	(15,000)
Stock-based compensation		(311,000)	294,000	302,000
Repurchase and retirement of common stock		(89,000)	(702,000)	(715,000)
Balance at the end of the period		101,207,000	100,994,000	101,416,000
Retained Earnings [Member]
Changes in the components of stockholders' equity
Balance at the beginning of the period		(36,968,000)	(38,826,000)	(42,858,000)
Net earnings		7,482,000	5,500,000	6,889,000
Dividends paid		$ (2,546,000)	$ (3,642,000)	$ (2,930,000)
Dividends paid (in dollars per share) | $ / shares		$ 0.07	$ 0.10	$ 0.08
Balance at the end of the period		$ (32,032,000)	$ (36,968,000)	$ (38,826,000)
Retained Earnings [Member] | ASU 2016-01
Changes in the components of stockholders' equity
Adoption of ASU 2016-01				73,000
Retained Earnings [Member] | ASU 2016-01 | Adjustment
Changes in the components of stockholders' equity
Adoption of ASU 2016-01					$ 73,000
Accumulated Other Comprehensive Income (Loss) [Member]
Changes in the components of stockholders' equity
Balance at the beginning of the period		(3,691,000)	(3,358,000)	(3,440,000)
Change in net actuarial loss and prior service cost, net of income tax expense		(94,000)	(333,000)	155,000
Balance at the end of the period		(3,785,000)	(3,691,000)	(3,358,000)
Income tax expense on change in net actuarial loss and prior service cost		$ 36,000	$ (135,000)	60,000
Accumulated Other Comprehensive Income (Loss) [Member] | ASU 2016-01
Changes in the components of stockholders' equity
Adoption of ASU 2016-01				$ (73,000)