Derivative Financial Instruments (Schedule of Derivative Offset Amounts) (Details) - USD ($) $ in Thousands		Mar. 31, 2020	Dec. 31, 2019
Derivative [Line Items]
Commodity derivatives deposits		$ 0	$ 27,415
Deposit Liability, Current		(50,345)	0
Exchange Traded [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability		(1,054)	(11,033)
Derivative Asset, Fair Value, Gross Asset		66,007	811
Derivative Liability, Fair Value, Amount Not Offset Against Collateral			(10,222)
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		64,953
Commodity derivatives deposits			27,415
Deposit Liability, Current		(50,345)
Amount After Offset	[1]	$ 14,608	$ 17,193

[1] Amount represents the maximum loss we would incur if all of our counterparties failed to perform on their derivative contracts.