Income Taxes Table 3 (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Asset (liability)
Post-employment benefits other than pensions	$ 1,626	$ 2,198
Other reserves	543	693
Deferred compensation	3,314	3,539
Environmental reserves	1,384	1,463
Inventory	2,740	3,032
Lease Obligations	4,614	0
Pensions	5,149	8,105
Accrued compensation expense	5,364	6,215
Net operating loss and credit carryforwards	13,513	12,002
Research and development tax credit carryforward	25	744
Foreign tax credit carryforward	0	2,385
Subtotal	38,272	40,376
Valuation allowance	(17,676)	(15,917)
Total deferred tax assets	20,596	24,459
Depreciation	(10,780)	(10,280)
Lease assets	(4,428)	0
Amortization	(2,426)	(3,635)
Mine development	(3,706)	(5,123)
Deferred Tax Liabilities, Gross	21,340	19,038
Deferred Tax Liability	$ (744)
Deferred Tax Assets, Net		$ 5,421