Earnings Per Share - Reconciliation of Components of Basic and Diluted Net Income Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net income (loss)	$ 57,105	$ 40,674	$ (20,555)	$ 47,488	$ 97,780	$ 26,933
Weighted average common shares outstanding - basic	197,514		197,054		197,449	196,803
Effect of dilutive instruments	555				640
Weighted average common shares outstanding - diluted	198,069		197,054		198,089	196,803
Net income (loss) per common share - basic	$ 0.29		$ (0.10)		$ 0.50	$ 0.14
Net income (loss) per common share - fully diluted	$ 0.29		$ (0.10)		$ 0.49	$ 0.14
Number of contingently issuable shares, including warrants, that are not included in the diluted earnings per share denominator as the performance or market criteria have not been met	20,218		2,636		20,109	2,636