Stockholders' Equity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Changes in the components of stockholders' equity
Balance at the beginning of the period	$ 115,008,000
Net earnings (loss)	786,000	$ 1,873,000	$ (706,000)
Unrealized gain on available-for-sale securities, net of income tax expense of $2, $4, $1	3,000	(6,000)	2,000
Repurchase and retirement of common stock	(66,000)	(65,000)	(104,000)
Balance at the end of the period	115,662,000	115,008,000
Income tax expense on change in pension net actuarial loss and prior service cost	261,000	318,000	2,365,000
Income tax expense on unrealized gain on available-for-sale securities	1,000	4,000	2,000
Common Stock | Common Stock
Changes in the components of stockholders' equity
Balance at the beginning of the period	1,799,000	1,788,000	1,774,000
Issuance of nonvested stock awards, net of forfeitures	22,000	18,000	21,000
Repurchase and retirement of common stock	(7,000)	(7,000)	(7,000)
Balance at the end of the period	1,814,000	1,799,000	1,788,000
Common Stock | Class A Common Stock
Changes in the components of stockholders' equity
Balance at the beginning of the period	1,487,000	1,487,000	1,487,000
Balance at the end of the period	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 period	5,424,000	5,125,000	4,663,000
Issuance of nonvested stock awards, net of forfeitures	(22,000)	(18,000)	(21,000)
Stock-based compensation	326,000	375,000	580,000
Repurchase and retirement of common stock	(59,000)	(58,000)	(97,000)
Balance at the end of the period	5,669,000	5,424,000	5,125,000
Retained Earnings
Changes in the components of stockholders' equity
Balance at the beginning of the period	110,502,000	108,629,000	109,335,000
Net earnings (loss)	786,000	1,873,000	(706,000)
Balance at the end of the period	111,288,000	110,502,000	108,629,000
Accumulated Other Comprehensive Loss
Changes in the components of stockholders' equity
Balance at the beginning of the period	(4,204,000)	(4,680,000)	(1,095,000)
Change in net actuarial loss and prior service cost, net of income tax benefit of $2,365, $318, $261	(395,000)	482,000	(3,588,000)
Unrealized gain on available-for-sale securities, net of income tax expense of $2, $4, $1	3,000	(6,000)	3,000
Balance at the end of the period	$ (4,596,000)	$ (4,204,000)	$ (4,680,000)