Revenue Recognition - Revenues from Contracts with Customers Disaggregated by Product (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	$ 1,405,220	$ 1,985,469	$ 2,143,716
Natural gas
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	1,404,989	1,985,240	1,881,150
Crude oil and condensate
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	0	0	48,722
Brokered natural gas
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	0	0	209,530
Other
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	$ 231	$ 229	$ 4,314