Stockholders' Equity (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	Jul. 28, 2004
Changes in the components of stockholders' equity
Balance at the beginning of the period			$ 53,805,000
Net earnings	$ 5,203,000	$ 5,066,000	2,798,000	$ 2,723,000
Unrealized gain on available-for-sale securities, net of income tax expense of $4	9,000	5,000	6,000	10,000
Change in net actuarial loss and prior service cost, net of income tax expense of $34	(25,000)	$ (18,000)	(50,000)	$ (35,000)
Balance at the end of the period	56,799,000		56,799,000
Income tax benefit on unrealized loss on available-for-sale securities			4,000
Income tax expense on change in net actuarial loss and prior service cost			34,000
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 of $2,328,000 and $2,362,000, respectively	(3,393,000)		(3,393,000)		$ (3,443,000)
Accumulated unrealized gain on available-for-sale securities, net of income tax expense of $41,000 and $37,000, respectively	57,000		57,000		51,000
Accumulated other comprehensive loss	(3,336,000)		(3,336,000)		(3,392,000)
Income tax benefit on net actuarial loss and prior service cost not yet recognized in net periodic benefit cost	2,328,000		2,328,000		2,362,000
Income tax expense on accumulated unrealized gain on available-for-sale securities	$ 41,000		$ 41,000		$ 37,000
Share Repurchase Authorization 2004
Accumulated other comprehensive loss, net of income taxes
Number of shares of common stock authorized to be repurchased						2,000,000
Number of shares purchased and retired			0	36,038
Average purchase price of shares purchased and retired (in dollars per share)				$ 2.22
Remaining number of shares authorized to be repurchased	1,140,318		1,140,318
Common Stock | Common Stock
Changes in the components of stockholders' equity
Balance at the beginning of the period			$ 1,828,000
Issuance of restricted stock awards, net of forfeitures			15,000
Repurchase and retirement of common stock			(5,000)
Balance at the end of the period	$ 1,838,000		1,838,000
Common Stock | Class A Common Stock
Changes in the components of stockholders' equity
Balance at the beginning of the period			1,851,000
Balance at the end of the period	1,851,000		1,851,000
Additional Paid-in Capital
Changes in the components of stockholders' equity
Balance at the beginning of the period			101,858,000
Issuance of restricted stock awards, net of forfeitures			(15,000)
Stock-based compensation			245,000
Repurchase and retirement of common stock			(100,000)
Balance at the end of the period	101,988,000		101,988,000
Accumulated Deficit
Changes in the components of stockholders' equity
Balance at the beginning of the period			(48,340,000)
Net earnings			2,798,000
Balance at the end of the period	(45,542,000)		(45,542,000)
Accumulated Other Comprehensive Loss
Changes in the components of stockholders' equity
Balance at the beginning of the period			(3,392,000)
Unrealized gain on available-for-sale securities, net of income tax expense of $4			6,000
Change in net actuarial loss and prior service cost, net of income tax expense of $34			50,000
Balance at the end of the period	$ (3,336,000)		$ (3,336,000)