Oil and Gas Properties and Equipment (Details) (USD $)	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Proven Properties [Abstract]
Acquisition, equipment, exploration, drilling and environmental costs	$ 8,108,781,000		$ 7,817,374,000
Capitalized Costs, Accumulated Depreciation, Depletion, Amortization and Valuation Allowance for Relating to Oil and Gas Producing Activities	(5,930,488,000)		(5,808,836,000)
Proved	2,178,293,000		2,008,538,000
Capitalized Costs of Unproved Properties Excluded from Amortization [Abstract]
Oil Gas Properties Using Full Cost Method Accounting Unproved	399,027,000		413,073,000
Capitalized Costs, Oil and Gas Producing Activities, Net	2,577,320,000		2,421,611,000
Property, Plant and Equipment [Abstract]
Gathering Systems	297,837,000		294,356,000
Accumulated Depreciation Gathering Systems	(107,258,000)		(105,246,000)
Net Gathering Systems	190,579,000		189,110,000
Other Property And Equipment	16,339,000		15,198,000
Accumulated Depreciation Other Property And Equipment	(10,334,000)		(9,758,000)
Net Other Property And Equipment	6,005,000		5,440,000
Land	23,107,000		22,359,000
Net Capitalized Costs Property Plant And Equipment	219,691,000		216,909,000
Interest Expense, Borrowings	65,300,000	51,400,000
Interest Costs, Capitalized During Period	$ 10,900,000	$ 400,000