Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	$ 633,424	$ 467,650
Gain on derivative instruments	8,257	5,577
TOTAL OPERATING REVENUES	641,681	473,227
Natural gas
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	633,174	412,108
Crude oil and condensate
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	0	48,722
Brokered natural gas
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	0	4,950
Other
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	$ 250	$ 1,870