Derivative Instruments - Fair Value of Derivative Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Derivative [Line Items]
Total Current Assets	$ 77,608	$ 247,794
Total Other Non-Current Assets	160,098	314,096
Total Current Liabilities	144,545	41,466
Total Non-Current Liabilities	203,709	115,862
Commodity Swap
Derivative [Line Items]
Total Current Assets	39,263	234,238
Total Other Non-Current Assets	118,210	288,543
Total Current Liabilities	103,297	345
Total Non-Current Liabilities	92,125	9,693
Basis Swap
Derivative [Line Items]
Total Current Assets	38,201	13,556
Total Other Non-Current Assets	41,060	25,553
Total Current Liabilities	36,878	40,626
Total Non-Current Liabilities	99,373	105,445
Interest Rate Swap
Derivative [Line Items]
Total Current Assets	144	0
Total Other Non-Current Assets	828	0
Total Current Liabilities	4,370	495
Total Non-Current Liabilities	$ 12,211	$ 724