Supplemental Gas and Oil Information - Unaudited Standardized Measure of Discounted Future Net Cash Flows (Details) - Non-Cost-of-Service Gas and Oil Reserves [Member] Mcfe in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) Mcfe	Dec. 31, 2014 USD ($) Mcfe
Discounted Future Net Cash Flows Relating to Non-Cost-of-Service Proved Reserves [Line Items]
Ending non-cost-of-service proved reserves (Mcfe) | Mcfe			10.4	36.6
Standardized Measure of Discounted Future Net Cash Flows Relating to Non-Cost-of-Service Proved Reserves [Abstract]
Future cash inflows			$ 29.5	$ 190.7
Future production costs			(15.7)	(65.9)
Future income tax expenses			(4.8)	(43.7)
Future net cash flows			9.0	81.1
10% annual discount for estimated timing of net cash flows			(3.6)	(34.4)
Standardized measure of discounted future net cash flows	$ 46.7	$ 0.0	$ 5.4	$ 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	46.7	0.0
Net increase due to purchases of reserves in place	6.0	46.8
Transfer to cost-of-service properties	(25.9)	0.0
Sales of gas and oil produced during the period, net of production costs	(8.4)	(1.5)
Net change in prices and production costs related to future production	(31.0)	0.8
Revisions of Previous Quantity Estimates	(0.4)	0.0
Accretion of discount	6.7	0.6
Changes in Future Income Tax Expense Estimates on Future Cash Flows Related to Proved Oil and Gas Reserves	11.7	0.0
Net Change	(41.3)	46.7
Balance at end of year	$ 5.4	$ 46.7