Supplemental Gas and Oil Information - Unaudited Standardized Measure of Discounted Future Net Cash Flows (Details) (Non-Cost-of-Service Gas and Oil Reserves [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 Mcfe
Non-Cost-of-Service Gas and Oil Reserves [Member]
Discounted Future Net Cash Flows Relating to Non-Cost-of-Service Proved Reserves [Line Items]
Ending non-cost-of-service proved reserves (Mcfe)	36,600,000
Standardized Measure of Discounted Future Net Cash Flows Relating to Non-Cost-of-Service Proved Reserves [Abstract]
Future cash inflows	$ 190.7
Future production costs	(65.9)
Future income tax expenses	(43.7)
Future net cash flows	81.1
10% annual discount for estimated timing of net cash flows	(34.4)
Standardized measure of discounted future net cash flows	46.7
Principal Sources of Change in Standardized Measure of Discounted Future Net Cash Flow Relating to Non-Cost-of-Service Proved Reserves [Abstract]
Balance at beginning of year	0
Net increase due to purchases of reserves in place	46.8
Sales of gas and oil produced during the period, net of production costs	(1.5)
Net change in prices and production costs related to future production	0.8
Accretion of discount	0.6
Net Change	46.7
Balance at end of year	$ 46.7