v3.10.0.1

Derivative Financial Instruments (Schedule of Derivative Offset Amounts) (Details) - Exchange Traded [Member] - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability		$ (7,155)	$ (38,936)
Derivative Asset, Fair Value, Gross Asset		62,166	12,851
Derivative Liability, Fair Value, Amount Not Offset Against Collateral			26,085
Derivative Asset, Fair Value, Amount Offset Against Collateral	[1]	55,011
Derivative, Right to Reclaim Cash			36,690
Derivative, Collateral, Obligation to Return Cash		(37,328)
Amount After Offset		$ 17,683	10,605
Other Current Liabilities [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral			25,694
Other Noncurrent Liabilities [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral			$ 391
[1] Net amount includes energy commodity derivative contracts classified as current liabilities of $25,694 and noncurrent liabilities of $391 at December 31, 2017.

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