Commitments and Contingencies (Details Textual) (USD $) In Millions, unless otherwise specified	12 Months Ended			120 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Feb. 28, 2015
Obligations (Textual)
Operating Leases, Rent Expense	$ 20.5	$ 19.9	$ 19.3
Lease Period For Office Space				10 years
Gas transportation and processing obligations [Member]
Obligations (Textual)
Operating Leases, Future Minimum Payments Due, Next Twelve Months	8.8
Operating Leases, Future Minimum Payments, Due in Two Years	8.0
Operating Leases, Future Minimum Payments, Due in Three Years	6.5
Operating Leases, Future Minimum Payments, Due in Four Years	3.7
Operating Leases, Future Minimum Payments, Due in Five Years	3.7
Operating Leases, Future Minimum Payments Due	36.2
Operating lease commitments [Member]
Obligations (Textual)
Operating Leases, Future Minimum Payments Due, Next Twelve Months	9.0
Operating Leases, Future Minimum Payments, Due in Two Years	1.3
Operating Leases, Future Minimum Payments, Due in Three Years	0.1
Operating Leases, Future Minimum Payments Due	$ 10.5