Income Taxes - Components of Deferred Income Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Reserve for receivables and inventories	$ 2,618	$ 2,108
Accrued compensation	1,874	888
Reserves & payables	2,741	1,410
Non-pension postretirement benefits	1,535	1,505
Net operating loss and credit carryforwards	2,106	1,401
Accrued pension benefits	982	933
Accrued employee benefits	1,574	1,747
Deferred revenue	2,596	2,219
Operating lease liabilities	1,708	1,861
Other	713	497
Total gross deferred tax assets	18,447	14,569
Less: valuation allowance	(2,140)	(863)
Total net deferred tax assets	16,307	13,706
Deferred tax liabilities:
Depreciation	5,204	4,673
Amortization	8,795	6,158
Prepaids	552	529
Operating lease assets	1,699	1,850
Other	663	630
Total deferred tax liabilities	16,913	13,840
Net deferred tax liabilities	$ (606)	$ (134)