Derivative Instruments - Fair Value of Derivative Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Derivative [Line Items]
Total Current Assets	$ 197,804	$ 247,794
Total Other Non-Current Assets	212,657	314,096
Total Current Liabilities	83,527	41,466
Total Non-current Liabilities	178,187	115,862
Commodity Swap
Derivative [Line Items]
Total Current Assets	187,567	234,238
Total Other Non-Current Assets	197,584	288,543
Total Current Liabilities	24,675	345
Total Non-current Liabilities	29,305	9,693
Basis Swap
Derivative [Line Items]
Total Current Assets	10,032	13,556
Total Other Non-Current Assets	13,851	25,553
Total Current Liabilities	54,711	40,626
Total Non-current Liabilities	136,140	105,445
Interest Rate Swap
Derivative [Line Items]
Total Current Assets	205	0
Total Other Non-Current Assets	1,222	0
Total Current Liabilities	4,141	495
Total Non-current Liabilities	$ 12,742	$ 724