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	Mar. 31, 2021	Dec. 31, 2020
Assets:
Gross Amount Recognized in the Statement of Financial Position	$ 52,146	$ 41,820
Gross Amounts Offset in the Statement of Financial Position	0	0
Assets	52,146	41,820
Commodity Contracts	(21,105)	(21,696)
Cash Collateral Received	0	0
Net Amount	31,041	20,124
Liabilities:
Gross Amount Recognized in the Statement of Financial Position	44,171	61,274
Gross Amounts Offset in the Statement of Financial Position	0	0
Derivative Liability	44,171	61,274
Commodity Contracts	(21,105)	(21,696)
Cash Collateral Posted	(143)	(9,343)
Net Amount	$ 22,923	$ 30,235