Income Taxes - Components of Deferred Income Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Reserve for receivables and inventories	$ 2,108	$ 2,210
Accrued compensation	888	929
Payables	1,410	1,090
Non-pension postretirement benefits	1,505	1,110
Net operating loss and credit carryforwards	1,401	308
Accrued pension benefits	933	1,552
Accrued employee benefits	1,747	2,534
Deferred revenue	2,219	1,858
Operating lease liabilities	1,861
Other	497
Total gross deferred tax assets	14,569	11,591
Less: valuation allowance	(863)	(366)
Total net deferred tax assets	13,706	11,225
Deferred tax liabilities:
Depreciation	4,673	4,679
Amortization	6,158	7,146
Prepaids	529	517
Operating lease assets	1,850
Other	630	52
Total deferred tax liabilities	13,840	12,394
Net deferred tax liabilities	$ (134)	$ (1,169)