Commitments and Contingencies (Narrative) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2016 USD ($)
Loss Contingencies [Line Items]
Overriding Royalty Interest	4.00%
Loss on Contingency, Estimate of Possible Loss, Minimum	$ 0.0
Loss Contingency, Estimate of Possible Loss, Maximum	60.0
Rocky Mountain Resources Lawsuit [Member]
Loss Contingencies [Line Items]
Litigation Settlement, Amount	$ 16.7
Litigation Settlement Statutory Interest Rate	10.00%
Loss Contingency Bond Posted	$ 20.0