Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Tax Credit Carryforward [Line Items]
Total net operating loss amount	$ 156,598
Operating loss carryforward expiration year 2021
Tax Credit Carryforward [Line Items]
Net operating loss amount	21,026
Operating loss carryforward expiration year 2022
Tax Credit Carryforward [Line Items]
Net operating loss amount	115,000
Operating loss carryforward expiration year 2023
Tax Credit Carryforward [Line Items]
Net operating loss amount	5,712
Operating loss carryforward expiration year 2024
Tax Credit Carryforward [Line Items]
Net operating loss amount	3,566
Operating loss carryforward expiration year 2025 and beyond [Member]
Tax Credit Carryforward [Line Items]
Net operating loss amount	$ 11,294