Derivative Financial Instruments - Summary of Pre-tax Realized and Unrealized Gain (Loss) Recognized Related to Derivative Instruments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Derivative [Line Items]
Unrealized gain (loss) on commodity derivatives			$ 82,527	$ (61,539)
Total gain (loss) on commodity derivatives	$ 71,654	$ (47,271)	7,316	(53,803)
Commodity Derivative Contract
Derivative [Line Items]
Unrealized gain (loss) on commodity derivatives	68,234	(53,933)	82,527	(61,539)
Total gain (loss) on commodity derivatives	71,654	(47,271)	7,316	(53,803)
Commodity Derivative Contract | Natural Gas
Derivative [Line Items]
Realized gain (loss) on commodity derivatives	3,936	10,982	(77,267)	12,426
Commodity Derivative Contract | Oil
Derivative [Line Items]
Realized gain (loss) on commodity derivatives	$ (516)	$ (4,320)	$ 2,056	$ (4,690)