Stockholders' Equity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in the components of stockholders' equity
Balance at the beginning of the year	$ 115,662,000
Net (loss) earnings	(1,068,000)	$ 786,000	$ 1,873,000
Unrealized gain (loss) on available-for-sale securities, net of income taxes of $4, $1 and $4 in 2017, 2016 and 2015 respectively	6,000	3,000	(6,000)
Repurchase and retirement of common stock	(74,000)	(66,000)	(65,000)
Balance at the end of the year	114,712,000	115,662,000
Income tax expense (benefit) on change in pension net actuarial loss and prior service cost	(72,000)	(261,000)	318,000
Income tax expense (benefit) on unrealized loss on available-for-sale securities	4,000	1,000	(4,000)
Common Stock | Common Stock
Changes in the components of stockholders' equity
Balance at the beginning of the year	1,814,000	1,799,000	1,788,000
Issuance of nonvested stock awards, net of forfeitures	20,000	22,000	18,000
Repurchase and retirement of common stock	(7,000)	(7,000)	(7,000)
Balance at the end of the year	1,827,000	1,814,000	1,799,000
Common Stock | Class A Common Stock
Changes in the components of stockholders' equity
Balance at the beginning of the year	1,487,000	1,487,000	1,487,000
Balance at the end of the year	1,487,000	1,487,000	1,487,000
Additional Paid-in Capital
Changes in the components of stockholders' equity
Balance at the beginning of the year	5,669,000	5,424,000	5,125,000
Issuance of nonvested stock awards, net of forfeitures	(20,000)	(22,000)	(18,000)
Stock-based compensation	295,000	326,000	375,000
Repurchase and retirement of common stock	(67,000)	(59,000)	(58,000)
Balance at the end of the year	5,877,000	5,669,000	5,424,000
Retained Earnings
Changes in the components of stockholders' equity
Balance at the beginning of the year	111,288,000	110,502,000	108,629,000
Net (loss) earnings	(1,068,000)	786,000	1,873,000
Balance at the end of the year	110,220,000	111,288,000	110,502,000
Accumulated Other Comprehensive Loss
Changes in the components of stockholders' equity
Balance at the beginning of the year	(4,596,000)	(4,204,000)	(4,680,000)
Change in net actuarial loss and prior service cost, net of income tax benefit of $72, $261, $318 in 2017, 2016 and 2015 respectively	(109,000)	(395,000)	482,000
Unrealized gain (loss) on available-for-sale securities, net of income taxes of $4, $1 and $4 in 2017, 2016 and 2015 respectively	6,000	3,000	(6,000)
Balance at the end of the year	$ (4,699,000)	$ (4,596,000)	$ (4,204,000)