Accounting for Derivative Instruments and Hedging Activities Net Amount of Derivatives Reported in the Statement of Financial Position (Details) - Commodity Contract [Member] - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Assets:
Gross Amount Recognized in the Statement of Financial Position	$ 362,527	$ 41,820
Gross Amounts Offset in the Statement of Financial Position	0	0
Assets	362,527	41,820
Commodity Contracts	(48,450)	(21,696)
Cash Collateral Received	0	0
Net Amount	314,077	20,124
Liabilities:
Gross Amount Recognized in the Statement of Financial Position	62,454	61,274
Gross Amounts Offset in the Statement of Financial Position	0	0
Derivative Liability	62,454	61,274
Commodity Contracts	(48,450)	(21,696)
Cash Collateral Posted	(62)	(9,343)
Net Amount	$ 13,942	$ 30,235