Stockholders' Equity (Details)		12 Months Ended
	Jun. 14, 2016	Dec. 31, 2019 USD ($) Vote $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares	Jan. 01, 2018 USD ($)
Changes in the components of stockholders' equity
Balance at the beginning of the period		$ 62,888,000
Net earnings		5,500,000	$ 6,889,000	$ 8,426,000
Dividends paid		3,642,000	2,930,000	2,944,000
Unrealized gain on equity investments, net of income taxes				22,000
Change in net actuarial loss and prior service cost, net of income tax expense		(333,000)	155,000	(70,000)
Balance at the end of the period		$ 63,968,000	$ 62,888,000
Preferred stock, shares issued | shares		0	0
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 of $2,485,000, and $2,350,000, respectively		$ (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		$ 2,485,000	2,350,000
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%
Class A Common Stock
Changes in the components of stockholders' equity
Number of votes per share | Vote		10
Common Stock
Changes in the components of stockholders' equity
Balance at the beginning of the period		$ 1,805,000	1,825,000	1,828,000
Issuance of restricted stock awards, net of forfeitures		14,000	15,000	15,000
Repurchase and retirement of common stock		(37,000)	(35,000)	(18,000)
Balance at the end of the period		$ 1,782,000	1,805,000	1,825,000
Number of votes per share | Vote		1
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
Balance at the end of the period		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		101,416,000	101,844,000	101,858,000
Issuance of restricted stock awards, net of forfeitures		(14,000)	(15,000)	(15,000)
Stock-based compensation		(294,000)	302,000	364,000
Repurchase and retirement of common stock		(702,000)	(715,000)	(363,000)
Balance at the end of the period		100,994,000	101,416,000	101,844,000
Accumulated Deficit
Changes in the components of stockholders' equity
Balance at the beginning of the period		(38,826,000)	(42,858,000)	(48,340,000)
Net earnings		5,500,000	6,889,000	8,426,000
Dividends paid		$ (3,642,000)	$ (2,930,000)	$ (2,944,000)
Dividends paid (in dollars per share) | $ / shares		$ 0.10	$ 0.08	$ 0.08
Balance at the end of the period		$ (36,968,000)	$ (38,826,000)	$ (42,858,000)
Accumulated Deficit | ASU 2016-01
Changes in the components of stockholders' equity
Adoption of ASU 2016-01			73,000
Accumulated Deficit | ASU 2016-01 | Adjustment
Changes in the components of stockholders' equity
Adoption of ASU 2016-01					$ 73,000
Accumulated Other Comprehensive Loss
Changes in the components of stockholders' equity
Balance at the beginning of the period		(3,358,000)	(3,440,000)	(3,392,000)
Unrealized gain on equity investments, net of income taxes				22,000
Change in net actuarial loss and prior service cost, net of income tax expense		(333,000)	155,000	(70,000)
Balance at the end of the period		(3,691,000)	(3,358,000)	(3,440,000)
Income tax expense (benefit) on unrealized gain (loss) on available-for-sale securities				15,000
Income tax benefit (expense) on change in net actuarial loss and prior service cost		$ 135,000	(60,000)	$ 48,000
Accumulated Other Comprehensive Loss | ASU 2016-01
Changes in the components of stockholders' equity
Adoption of ASU 2016-01			$ (73,000)
Accumulated Other Comprehensive Loss | ASU 2016-01 | Adjustment
Changes in the components of stockholders' equity
Adoption of ASU 2016-01					$ (73,000)