Income Taxes (Summary of Operating Loss Carryforwards and Tax Credit Carryforwards) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Net deferred tax asset, net operating loss	$ 22,035	$ 21,527
Total net deferred tax asset	25,591	26,820
Total valuation allowance	14,492	14,082
Foreign tax authority
Operating Loss Carryforwards [Line Items]
Net deferred tax asset, net operating loss	1,438	732
Valuation allowance, net operating loss	1,438	732
State and local jurisdiction
Operating Loss Carryforwards [Line Items]
Net deferred tax asset, net operating loss	16,948	15,299
Valuation allowance, net operating loss	13,054	13,350
Net deferred tax asset, tax credit carryforwards, research	1,870	2,754
Net deferred tax asset, alternative minimum tax credit	5,335	8,035
Valuation allowance, tax credit	$ 0	$ 0