Income Taxes (Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets
Accrued employee benefits and compensation	$ 6,199	$ 5,730
Tax loss and credit carryforwards	17,644	17,761
Reserves and accruals	6,581	5,996
Operating leases	665	904
Capitalized research and development	14,167	11,343
Other	1,824	2,210
Total deferred tax assets	47,080	43,944
Less deferred tax asset valuation allowance	(9,250)	(14,625)	$ (16,889)	$ (8,754)
Total deferred tax assets, net of valuation allowance	37,830	29,319
Deferred tax liabilities
Depreciation and amortization	10,282	15,368
Postretirement benefit obligations	2,001	1,719
Unremitted earnings	2,426	1,624
Operating leases	714	908
Other	2,115	1,803
Total deferred tax liabilities	17,538	21,422
Net deferred tax asset (liability)	$ 20,292	$ 7,897