Derivative Instruments - Schedule of Location and Fair Value of Outstanding Commodity Derivative Instruments (Details) - Commodity derivative instruments - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Derivative asset, gross amounts recognized	$ 80,006	$ 118,980
Derivative liability, gross amount recognized	1,428	104
Derivative asset, gross amounts offset	(18,097)	(12,105)
Derivative liability, gross amounts offset	(598)	0
Derivative asset, net asset	61,909	106,875
Derivative liability, net liability	830	104
Current assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amounts recognized	63,743	110,729
Derivative asset, gross amounts offset	(11,563)	(10,799)
Derivative asset, net asset	52,180	99,930
Noncurrent assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amounts recognized	16,263	8,251
Derivative asset, gross amounts offset	(6,534)	(1,306)
Derivative asset, net asset	9,729	6,945
Current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	1,428	84
Derivative liability, gross amounts offset	(598)	0
Derivative liability, net liability	830	84
Noncurrent liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	0	20
Derivative liability, gross amounts offset	0	0
Derivative liability, net liability	$ 0	$ 20