Acquisitions (Details) (USD $)	12 Months Ended
	Dec. 31, 2013 acre	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Allegheny County Airport Lease [Member] acre	Dec. 31, 2013 Dominion Acquisition Member	Dec. 31, 2013 Ryerson Park Lake and Dam [Member]	Dec. 31, 2012 Ryerson Park Lake and Dam [Member] acre	Dec. 31, 2013 Potomac coal reserves [Member]	Dec. 31, 2012 Antero [Member]	Sep. 30, 2012 Antero [Member] acre
Business Acquisition [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Range of Outcomes, Contingent Consideration, Liability, Value, High					$ 190,000,000	$ 36,000,000
Reimbursement From JV Partner				0.50
Bonus Payment						13,728,000
Coal Lands and or Surface Rights							506,000
Gas and Oil Area, Undeveloped, Gross	105,019,000			9,000
Acquisition Costs, Period Cost					91,243,000
Proceeds from Sale of Property, Plant, and Equipment								25,000,000	193,000
Gas and Oil Acreage, Unproved, Net	4,212,030,000									116
Business Acquisition, Cost of Acquired Entity, Transaction Costs				46,315,000					2,619
Escrow Deposit				0.076
Acquisition and Financing Fees	$ 0	$ 0	$ 14,907,000