Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 333,294	$ 418,051	$ 992,063	$ 1,521,943
Natural gas
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	333,256	418,133	991,882	1,521,789
Other
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 38	$ (82)	$ 181	$ 154