Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Income Taxes [Line Items]
Federal Statutory Rate					21.00%	21.00%	24.50%	35.00%
Reduction to Income Tax Expense Due to Remeasurement of Deferred Income Tax Assets and Liabilites	$ (5,000)	$ 3,500	$ 4,000	$ (111,000)		$ (5,000)	$ (103,500)
Reduction In Deferred Taxes for Rate Regulated Activities Due to Remeasurement of Deferred Income Tax Assets and Liabilities							336,700
Decrease To Recoverable Future Taxes Impact of Change In Corporate Tax Rate							65,700
Increase in Taxes Refundable To Customers Due to Changes In Corporate Tax Rate							271,000
Taxes Refundable to Customers		370,628			$ 370,628	366,503	370,628
Recoverable Future Taxes		115,460			115,460	115,197	115,460
Deferred Income Taxes [Member]
Income Taxes [Line Items]
Taxes Refundable to Customers		370,600			370,600	366,500	370,600
Recoverable Future Taxes		115,500			115,500	115,200	115,500
Federal [Member]
Income Taxes [Line Items]
Income Taxes Receivable		22,457			22,457	42,388	22,457
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Income Taxes Receivable		8,822			8,822	8,579	8,822
Alternative Minimum Tax Credit [Member]
Income Taxes [Line Items]
Tax Credit Carryforwards		$ 85,000			$ 85,000		$ 85,000
Alternative Minimum Tax Credit [Member] | California [Member]
Income Taxes [Line Items]
Tax Credit Carryforwards						7,711
Alternative Minimum Tax Credit [Member] | Federal [Member]
Income Taxes [Line Items]
Tax Credit Carryforwards						42,546
Guidance for Stock Based Compensation [Member]
Income Taxes [Line Items]
Cumulative Effect of Adoption of Authoritative Guidance								$ 31,900
Other Current Assets [Member] | Federal [Member]
Income Taxes [Line Items]
Income Taxes Receivable						$ 42,500