Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Tax loss carryforwards	$ 50,183	$ 62,994
Tax credit carryforwards	792	19
Uniform capitalization, contract and inventory related reserves	805	598
Accrued vacation	301	514
Stock-based compensation	2,029	2,130
Capitalized research and development	3,043	5,532
Tax basis depreciation less book depreciation	1,523	1,661
Intangible assets	0	1,354
Deferred revenue	175	33
Accrued foreign taxes	1,044	1,263
Other	2,369	2,523
Total	62,264	78,621
Deferred tax liabilities:
Inventory deduction	(587)	(369)
Pension assets	(1,326)	(1,733)
Allowance for doubtful accounts	(534)	(677)
Withholding tax on undistributed earnings of foreign subsidiary	(4,879)	(4,879)
Unrealized gains and losses	(351)	(733)
Intangible assets	(1,514)	0
Total	(9,191)	(8,391)
Net deferred tax assets before valuation allowance	53,073	70,230
Valuation allowance	(61,403)	(78,366)
Net deferred tax liabilities	$ (8,330)	$ (8,136)