Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	$ 288,374	$ 470,468	$ 658,769	$ 1,103,892
Natural gas
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	288,286	470,482	658,626	1,103,656
Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	$ 88	$ (14)	$ 143	$ 236