Derivative Financial Instruments - Summary of Pre-tax Realized and Unrealized Gain (Loss) Recognized Related to Derivative Instruments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Derivative [Line Items]
Unrealized gain (loss) on commodity derivatives	$ 14,292	$ (7,606)
Total gain (loss) on commodity derivatives	(64,339)	(6,530)
Commodity Derivative Contract
Derivative [Line Items]
Unrealized gain (loss) on commodity derivatives	14,292	(7,606)
Total gain (loss) on commodity derivatives	(64,339)	(6,530)
Commodity Derivative Contract | Natural Gas
Derivative [Line Items]
Realized gain (loss) on commodity derivatives	(81,203)	1,446
Commodity Derivative Contract | Oil
Derivative [Line Items]
Realized gain (loss) on commodity derivatives	$ 2,572	$ (370)