Contingencies (Narrative) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2016 USD ($)
Rocky Mountain Resources Lawsuit [Member]
Loss Contingencies [Line Items]
Loss Contingency, Range of Possible Loss, Minimum	$ 0.0
Loss Contingency, Range of Possible Loss, Maximum	20.0
Litigation Settlement, Amount	$ 16.7
Litigation Settlement Statutory Interest Rate	10.00%
Loss Contingency Bond Posted	$ 20.0
Gas Purchase Agreement Arbitration [Member]
Loss Contingencies [Line Items]
Loss Contingency, Range of Possible Loss, Minimum	0.0
Loss Contingency, Range of Possible Loss, Maximum	$ 2.5