Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	$ 470,468	$ 457,115	$ 1,103,892	$ 924,765
Gain (loss) on derivative instruments	63,649	(3,668)	71,906	1,909
Total operating revenues	534,117	453,447	1,175,798	926,674
Natural gas
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	470,482	364,660	1,103,656	776,768
Crude oil and condensate
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	0	0	0	48,722
Brokered natural gas
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	0	92,576	0	97,526
Other
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	$ (14)	$ (121)	$ 236	$ 1,749

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The difference between the book value and the sale price of options, swaps, futures, forward contracts, and other derivative instruments. This element refers to the gain (loss) included in earnings.

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Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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