Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Details 3) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Significant components of deferred tax assets and liabilities
Post-retirement benefits	$ 1,061	$ 1,160
Inventory reserves	1,236	1,128
Loss carry-forwards	4,647	5,401
Credit carry-forwards	16,909	10,793
Nondeductible accruals	5,685	7,062
Research expenditures	16,847	20,002
Stock compensation	2,142	1,803
Foreign exchange loss	2,245	1,373
Other	207	220
Gross deferred tax assets	50,979	48,942
Depreciation and amortization	11,500	9,819
Pensions	11,736	12,387
Subsidiaries' unremitted earnings	1,258	1,662
Gross deferred tax liabilities	24,494	23,868
Net deferred tax assets	26,485	25,074
Deferred tax asset valuation allowance	(8,274)	(8,182)
Total net deferred tax assets	$ 18,211	$ 16,892