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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Derivative [Line Items]
Unrealized gain (loss) on commodity derivatives			$ (61,539)	$ 8,367
Total gain (loss) on commodity derivatives	$ (47,271)	$ 20,717	(53,803)	7,499
Commodity Derivative Contract
Derivative [Line Items]
Unrealized gain (loss) on commodity derivatives	(53,933)	21,585	(61,539)	8,367
Total gain (loss) on commodity derivatives	(47,271)	20,717	(53,803)	7,499
Commodity Derivative Contract | Natural Gas
Derivative [Line Items]
Realized gain (loss) on commodity derivatives	10,982	$ (868)	12,426	$ (868)
Commodity Derivative Contract | Oil
Derivative [Line Items]
Realized gain (loss) on commodity derivatives	$ (4,320)		$ (4,690)