Acquisitions (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013 acre
Business Acquisition [Line Items]
Gas and Oil Area, Undeveloped, Gross	112,617,000
Columbia Energy Ventures [Member]
Business Acquisition [Line Items]
Business Acquisition, Cost of Acquired Entity, Transaction Costs	$ 96,000
Other Liabilities, Current	49,533
Other Long-term Debt, Noncurrent	40,286
Allegheny County Airport Lease [Member]
Business Acquisition [Line Items]
Reimbursement From JV Partner	0.50
Gas and Oil Area, Undeveloped, Gross	9,000
Business Acquisition, Cost of Acquired Entity, Transaction Costs	46,315,000
Escrow Deposit	0.076
Dominion Acquisition Member
Business Acquisition [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Range of Outcomes, Contingent Consideration, Liability, Value, High	190,000,000
Bonus Payment	16,000
Acquisition Costs, Period Cost	91,243,000
Ryerson Park Lake and Dam [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Range of Outcomes, Contingent Consideration, Liability, Value, High	36,000,000
Bonus Payment	13,728,000
Coal Lands and or Surface Rights		506,000
Marshall County WV Utica Assets [Member]
Business Acquisition [Line Items]
Gas and Oil Area, Undeveloped, Gross	1,700,000
Gain (Loss) on Sale of Property Plant Equipment	25,000
Burning Star 5 Sale [Member] [Member]
Business Acquisition [Line Items]
Proceeds from Sale of Property, Plant, and Equipment	25,000
Gain (Loss) on Sale of Property Plant Equipment	22,000
Potomac coal reserves [Member]
Business Acquisition [Line Items]
Proceeds from Sale of Property, Plant, and Equipment	25,000,000
Gain (Loss) on Sale of Property Plant Equipment	$ 24,663,000