Derivatives Derivates Impact on Income (Details) MMcf in Billions	12 Months Ended
	Dec. 31, 2016 USD ($) MMcf	Dec. 31, 2015 USD ($) MMcf	Dec. 31, 2014 USD ($)
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Cash Received on Hedge	$ 245,212,000	$ 196,348,000	$ 19,025,000
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	(386,233,000)	196,594,000	4,168,000
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(43,470,000)		(18,288,000)
Derivative Instruments, Loss Reclassified from Accumulated OCI into Income, Effective Portion	0	0	97,316,000
Accumulated Other Comprehensive Income (Loss), Net of Tax	(392,556,000)	(315,598,000)
Accumulated Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax [Roll Forward]
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	43,470,000	121,521,000	42,493,000
Gain (Loss) on Hedging Activity	$ (141,021,000)	$ 392,942,000	23,193,000
Commodity Member [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | MMcf	0.0	456.1
Reclassification out of Accumulated Other Comprehensive Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	$ 68,481,000	$ 123,105,000	0
Accumulated Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax [Roll Forward]
Gain (Loss) on Hedging Activity	68,481,000	123,105,000	0
ineffectiveness member [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	0	0	4,168,000
Accumulated Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax [Roll Forward]
Gain (Loss) on Hedging Activity	0	0	4,168,000
Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Cash Received on Hedge	(225,797,000)	(193,976,000)	(19,025,000)
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	(520,170,000)	81,142,000	0
Accumulated Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax [Roll Forward]
Gain (Loss) on Hedging Activity	(294,373,000)	275,118,000	19,025,000
Natural Gas Liquids [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Cash Received on Hedge	650,000	0	0
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	(1,148,000)	0	0
Accumulated Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax [Roll Forward]
Gain (Loss) on Hedging Activity	(1,798,000)	0	0
Basis Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Cash Received on Hedge	(20,065,000)	(2,372,000)	0
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	66,604,000	(7,653,000)	0
Accumulated Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax [Roll Forward]
Gain (Loss) on Hedging Activity	$ 86,669,000	$ (5,281,000)	0
Basis Member [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | MMcf	482.0	124.4
Propane [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | MMcf	126.0	0.0
Natural Gas [Member] | Swap [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ 0	$ 43,470,000	121,521,000
Revenue Mineral Sales [Member] | Natural Gas [Member] | Swap [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ (43,470,000)	$ (78,051,000)	$ (18,288,000)