Income Taxes (Schedule of Federal Net Operating Losses and Tax Credit Carryforwards) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Net Operating Losses	$ 142,619
Research and Development Tax Credits	2,438	$ 2,338
2018-2020 [Member]
Operating Loss Carryforwards [Line Items]
Net Operating Losses	30,281
Research and Development Tax Credits	809
2021-2024 [Member]
Operating Loss Carryforwards [Line Items]
Net Operating Losses	41,283
2025-2037 [Member]
Operating Loss Carryforwards [Line Items]
Net Operating Losses	71,055
Research and Development Tax Credits	$ 1,629
Minimum [Member] | 2018-2020 [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforward, expiration	Jan. 01, 2018
Minimum [Member] | 2021-2024 [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforward, expiration	Jan. 01, 2021
Minimum [Member] | 2025-2037 [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforward, expiration	Jan. 01, 2025
Maximum [Member] | 2018-2020 [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforward, expiration	Dec. 31, 2020
Maximum [Member] | 2021-2024 [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforward, expiration	Dec. 31, 2024
Maximum [Member] | 2025-2037 [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforward, expiration	Dec. 31, 2037