Income Taxes - Components of Deferred Income Taxes (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Reserve for receivables and inventories	$ 2,405,000	$ 2,931,000
Accrued compensation	861,000	1,131,000
Payables	886,000	1,107,000
Non-pension postretirement benefits	1,561,000	2,344,000
Net operating loss and credit carryforwards	364,000	968,000
Accrued pension benefits	1,071,000	413,000
Accrued employee benefits	3,219,000	4,103,000
Deferred revenue	1,504,000	0
Other	450,000	487,000
Total gross deferred tax assets	12,321,000	13,484,000
Less: valuation allowance	(373,000)	0
Total net deferred tax assets	11,948,000	13,484,000
Depreciation	3,778,000	5,126,000
Amortization	8,266,000	8,992,000
Prepaids	482,000	567,000
Total deferred tax liabilities	12,526,000	14,685,000
Net deferred tax (liabilities)	$ (578,000)
Net deferred tax assets		$ (1,201,000)