Income Taxes (Schedule of Federal Net Operating Losses and Tax Credit Carryforwards) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Operating Loss Carryforwards [Line Items]
Net Operating Losses	$ 131,863
Research and Development Tax Credits	2,450	$ 2,479
2020-2021 [Member]
Operating Loss Carryforwards [Line Items]
Net Operating Losses	28,171
Research and Development Tax Credits	323
2022-2025 [Member]
Operating Loss Carryforwards [Line Items]
Net Operating Losses	42,814
Research and Development Tax Credits	319
2026-2037 [Member]
Operating Loss Carryforwards [Line Items]
Net Operating Losses	45,866
Research and Development Tax Credits	1,808
No Expiration [Member]
Operating Loss Carryforwards [Line Items]
Net Operating Losses	$ 15,012
Minimum [Member] | 2020-2021 [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforward, expiration	Jan. 01, 2020
Minimum [Member] | 2022-2025 [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforward, expiration	Jan. 01, 2022
Minimum [Member] | 2026-2037 [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforward, expiration	Jan. 01, 2026
Maximum [Member] | 2020-2021 [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforward, expiration	Dec. 31, 2021
Maximum [Member] | 2022-2025 [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforward, expiration	Dec. 31, 2025
Maximum [Member] | 2026-2037 [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforward, expiration	Dec. 31, 2037