Derivative Instruments - Effect of Derivative Instruments on Consolidated Statement of Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Cash received (paid) on settlement of derivative instruments	$ 35,218	$ 138,450	$ (41,631)
Non-cash gain (loss) on derivative instruments	26,186	(57,642)	86,063
Total	$ 61,404	$ 80,808	$ 44,432