Summary of Significant Accounting Policies - Property and equipment (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) item	Dec. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($)
Property and Equipment
Depreciation expense	$ 972,465	$ 824,610	$ 809,873
Oil and Gas Properties
Exploratory drilling costs initially capitalized, but subsequently charged to expense	0	0	0
Impairment of unproved properties for leases expired or expected to expire	549,000	160,000	163,000
Impairment of proved properties	0
Depreciation, depletion, and amortization expense for oil and gas properties	832,000	694,000	700,000
Asset Impairment Charges	$ 9,658	$ 23,431	0
Number of imbalance positions | item	0	0
Deferred Financing Costs
Unamortized deferred financing costs included in long-term debt	$ 35,000
Unamortized deferred financing costs included in other assets	19,000
Amounts amortized and the write-off of previously deferred debt issuance costs	$ 13,000	$ 13,000	16,000
Gathering Systems and Facilities
Property and Equipment
Estimated useful life	P50Y
Other property and equipment
Property and Equipment
Depreciation expense	$ 9,000	10,000	9,000
Other property and equipment | Minimum
Property and Equipment
Estimated useful life	P2Y
Other property and equipment | Maximum
Property and Equipment
Estimated useful life	P20Y
Gathering pipelines, compressor stations, and fresh water distribution systems
Property and Equipment
Depreciation expense	$ 131,000	$ 120,000	$ 101,000
Water handling and treatment | Minimum
Property and Equipment
Estimated useful life	P5Y
Water handling and treatment | Maximum
Property and Equipment
Estimated useful life	P20Y