Summary of Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	$ 2,143,716	$ 1,747,293	$ 1,194,627
Gain (loss) on derivative instruments	44,432	16,926	(38,950)
TOTAL OPERATING REVENUES	2,188,148	1,764,219	1,155,677
Natural gas
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	1,881,150	1,506,078	1,022,590
Crude oil and condensate
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	48,722	212,338	151,106
Brokered natural gas
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	209,530	17,217	13,569
Other
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	$ 4,314	$ 11,660	$ 7,362