Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Details 3) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Significant components of deferred tax assets and liabilities
Post-retirement benefits	$ 1,798	$ 1,837
Inventory reserves	1,834	1,797
Loss carry-forwards	7,279	9,387
Credit carry-forwards	22,743	35,082
Nondeductible accruals	11,629	12,406
Research expenditures	31,380	30,465
Stock compensation	2,681	2,070
Foreign exchange loss	1,780	2,522
Other	648	1,231
Gross deferred tax assets	81,772	96,797
Depreciation and amortization	9,960	9,814
Pensions	16,024	11,868
Subsidiaries' unremitted earnings	1,292	7,461
Gross deferred tax liabilities	27,276	29,143
Net deferred tax assets	54,496	67,654
Deferred tax asset valuation allowance	(11,024)	(10,266)
Total net deferred tax assets	$ 43,472	$ 57,388