Derivative Financial Instruments - Summary of Pre-tax Realized and Unrealized Gain (Loss) Recognized Related to Derivative Instruments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative [Line Items]
Unrealized gain (loss) on commodity derivatives			$ (72,557)	$ 4,133
Total gain (loss) on commodity derivatives	$ (21,804)	$ 4,650	(75,607)	12,149
Commodity Derivative Contract
Derivative [Line Items]
Unrealized gain (loss) on commodity derivatives	(11,018)	(4,234)	(72,557)	4,133
Total gain (loss) on commodity derivatives	(21,804)	4,650	(75,607)	12,149
Commodity Derivative Contract | Natural Gas
Derivative [Line Items]
Realized gain (loss) on commodity derivatives	(5,468)	$ 8,884	6,958	$ 8,016
Commodity Derivative Contract | Oil
Derivative [Line Items]
Realized gain (loss) on commodity derivatives	$ (5,318)		$ (10,008)