Subsequent Event Subsequent Events (Details) - USD ($) $ in Millions		3 Months Ended
	Apr. 08, 2016	Mar. 31, 2016
Subsequent Event [Line Items]
Credit facility maximum credit amount		$ 900.0
Leverage ratio of long-term debt		4 to 1
Future discounted net cash flows discounted		10.00%
Subsequent Event [Member]
Subsequent Event [Line Items]
Credit facility maximum credit amount	$ 875.0
Commitment fee percentage under credit facility	0.50%
Line Of Credit Facility Commitment Amount [Member]
Subsequent Event [Line Items]
Credit facility current credit amount		$ 500.0
Line Of Credit Facility Commitment Amount [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Credit facility current credit amount	$ 475.0
Line Of Credit Facility Lender Determined Amount [Member]
Subsequent Event [Line Items]
Credit facility current credit amount		$ 550.0
Line Of Credit Facility Lender Determined Amount [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Credit facility current credit amount	$ 475.0
Apr 8, 2016 to Mar 31, 2019 [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Senior indebtedness ratio	2.75 to 1.0
Apr 1, 2019 to Apr 10, 2020 [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Leverage ratio of long-term debt	4.0 to 1.0
Collateral Pledged [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Percentage of proved developed properties pledged as collateral	85.00%
Future discounted net cash flows discounted	8.00%
Ownership percentage of Superior Pipeline Company, L.L.C. pledged as collateral	100.00%
Minimum [Member]
Subsequent Event [Line Items]
LIBOR plus interest rate		1.75%
Commitment fee percentage under credit facility		0.375%
Minimum [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Interest rate in addition to base rate	1.00%
LIBOR plus interest rate	2.00%
Maximum [Member]
Subsequent Event [Line Items]
LIBOR plus interest rate		2.50%
Commitment fee percentage under credit facility		0.50%
Maximum [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Interest rate in addition to base rate	3.00%
LIBOR plus interest rate	3.00%