Stockholders' Equity (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Changes in the components of stockholders' equity
Balance at the beginning of the period			$ 115,008,000
Net earnings	$ 796,000	$ 631,000	557,000	$ 279,000
Unrealized gain on available-for-sale securities, net of income tax expense of $3	1,000	$ (2,000)	3,000	2,000
Repurchase and retirement of common stock			(66,000)	$ (65,000)
Balance at the end of the period	115,720,000		115,720,000
Class A common stock
Changes in the components of stockholders' equity
Balance at the beginning of the period			1,487,000
Balance at the end of the period	1,487,000		1,487,000
Common Stock
Changes in the components of stockholders' equity
Balance at the beginning of the period			1,799,000
Issuance of nonvested stock awards, net of forfeitures			22,000
Repurchase and retirement of common stock			(7,000)
Balance at the end of the period	1,814,000		1,814,000
Additional Paid-in Capital
Changes in the components of stockholders' equity
Balance at the beginning of the period			5,424,000
Issuance of nonvested stock awards, net of forfeitures			(22,000)
Stock-based compensation			177,000
Repurchase and retirement of common stock			(59,000)
Balance at the end of the period	5,520,000		5,520,000
Retained Earnings
Changes in the components of stockholders' equity
Balance at the beginning of the period			110,502,000
Net earnings			557,000
Balance at the end of the period	111,059,000		111,059,000
Accumulated Other Comprehensive Loss
Changes in the components of stockholders' equity
Balance at the beginning of the period			(4,204,000)
Change in net actuarial loss and prior service cost, net of income tax expense of $27			41,000
Unrealized gain on available-for-sale securities, net of income tax expense of $3			3,000
Balance at the end of the period	$ (4,160,000)		(4,160,000)
Income tax expense on change in pension net actuarial loss and prior service cost			27,000
Income tax expense on unrealized gain on available-for-sale securities			$ 3,000