Commitments and Contingencies (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) MMBTU	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Commitements And Contingencies Disclosure [Abstract]
Total interest expense contractual obligation	$ 906.6
Interest expense due in one year	168.6
Interest expense due in two to three years	287.6
Interest expense due in three to five years	184.5
Interest expense due in five or more years	$ 265.9
Commitment capacity per day of natural gas | MMBTU	200
Increased commitment capacity per day of natural gas | MMBTU	50
Demand charges related to remaining contract	$ 368.1
Initial Term Liquids Gathering System Lease	15
Renewal Term Liquids Gathering System Lease	5
Renewal Term Liquids Gathering System Lease Useful Life	75.00%
Liquids Gathering System Operating Lease Rental Expense	$ 20.0
Lease And Rental Expense Total	248.2
Office Space Operating Lease Total Future Minimum Payments	7.8
Commitment to office leases, current	1.4
Commitment to office leases, due in two years	1.4
Commitment to office leases, due in three years	1.3
Commitment to office leases, due in four years	1.2
Commitment to office leases, due in five years	1.0
Office leases expense	$ 1.3	$ 1.0	$ 1.0
Oil and gas delivery commitments details	Delivery Commitments. With respect to the Company’s natural gas production, from time to time the Company enters into transactions to deliver specified quantities of gas to its customers. As of February 9, 2016, the Company has long-term natural gas delivery commitments of 5.1 MMMBtu in 2016 and 13.5 MMMBtu in 2017 under existing agreements. As of February 9, 2016, the Company has long-term crude oil delivery commitments of 3.4 MMBbls in 2016, 2.8 MMBbls in 2017, 1.1 MMBbls in 2018 and 0.2 MMBbls in 2019 under existing agreements. None of these commitments require the Company to deliver gas or oil produced specifically from any of the Company’s properties, and all of these commitments are priced on a floating basis with reference to an index price. In addition, none of the Company’s reserves are subject to any priorities or curtailments that may affect quantities delivered to its customers, any priority allocations or price limitations imposed by federal or state regulatory agencies or any other factors beyond the Company’s control that may affect its ability to meet its contractual obligations other than those discussed in Item 1A. “Risk Factors”. If for some reason our production is not sufficient to satisfy these commitments, subject to the availability of capital, we could purchase volumes in the market or make other arrangements to satisfy the commitments.