Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Significant components of deferred tax assets and liabilities
Post-retirement benefits	$ 1,226	$ 1,259
Inventory reserves	69	477
Loss carry-forwards	5,070	5,128
Credit carry-forwards	19,665	17,401
Accrued expenses	4,917	5,693
Research expenditures	19,226	18,893
Operating lease liabilities	5,643	6,012
Stock compensation	1,970	1,969
Foreign exchange loss	2,052	2,166
Other	769	872
Gross deferred tax assets	60,607	59,870
Depreciation and amortization	13,386	13,004
Pensions	10,958	12,557
Operating lease assets	5,307	5,703
Subsidiaries' unremitted earnings	1,947	3,046
Gross deferred tax liabilities	31,598	34,310
Net deferred tax assets	29,009	25,560
Deferred tax asset valuation allowance	(9,489)	(8,320)
Total net deferred tax assets	$ 19,520	$ 17,240