Income Taxes Income Taxes (Summary of Operating Loss and Tax Credit Carryforwards) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2018
Federal [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss, subject to expiration	$ 55,832
Net operating loss, not subject to expiration	83,356
Alternative Minimum Tax Credit [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards		$ 85,000
Research and Development Tax Credit Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	6,919
Enhanced Oil Recovery Credit [Member] | Federal [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	26,790
Pennsylvania [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss	385,093
California [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss	201,997
California [Member] | Alternative Minimum Tax Credit [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	8,737
California [Member] | Enhanced Oil Recovery Credit [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforwards	$ 7,903