Income Taxes (Summary of Operating Loss Carryforwards and Tax Credit Carryforwards) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Operating Loss Carryforwards [Line Items]
Net deferred tax asset, net operating loss	$ 17,756	$ 16,305
Total net deferred tax asset	21,356	20,045
Total valuation allowance	14,478	14,131
State and local jurisdiction
Operating Loss Carryforwards [Line Items]
Net deferred tax asset, net operating loss	18,708	16,531
Valuation allowance, net operating loss	14,478	13,668
Valuation allowance, tax credit		0
Net deferred tax asset, alternative minimum tax credit		1,596
Federal tax authority
Operating Loss Carryforwards [Line Items]
Net deferred tax asset, tax credit carryforwards, research	2,648	1,455
Valuation allowance, tax credit	$ 0	0
Foreign tax authority
Operating Loss Carryforwards [Line Items]
Valuation allowance, tax credit		463
Net deferred tax asset, federal foreign tax credit		$ 463