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	Jun. 30, 2020	Dec. 31, 2019
Assets:
Gross Amount Recognized in the Statement of Financial Position	$ 34,543	$ 31,308
Gross Amounts Offset in the Statement of Financial Position	0	0
Assets	34,543	31,308
Commodity Contracts	(24,528)	(14,922)
Cash Collateral Received	0	0
Net Amount	10,015	16,386
Liabilities:
Gross Amount Recognized in the Statement of Financial Position	63,941	26,121
Gross Amounts Offset in the Statement of Financial Position	0	0
Derivative Liability	63,941	26,121
Commodity Contracts	(24,528)	(14,922)
Cash Collateral Posted	0	2,000
Net Amount	$ 39,413	$ 13,199