Earnings Per Share - Summary (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Basic:
Net Income (Loss)	$ 6,278	$ (603,247)	$ (545,906)	$ (772,553)
Less: net loss allocable to participating RSUs	0	0	0	0
Net income (loss) available for basic common shares	$ 6,278	$ (603,247)	$ (545,906)	$ (772,553)
Weighted average common shares outstanding	345,285	343,870	344,774	343,304
Basic net loss per common share (USD per share)	$ 0.02	$ (1.75)	$ (1.58)	$ (2.25)
Diluted:
Net Income (Loss)	$ 6,278	$ (603,247)	$ (545,906)	$ (772,553)
Less: net loss allocable to participating RSUs	0	0	0	0
Net income (loss) available for diluted common shares	$ 6,278	$ (603,247)	$ (545,906)	$ (772,553)
Weighted average common shares outstanding	345,285	343,870	344,774	343,304
Weighted average common equivalent shares arising from:
Dilutive stock options and non-participating RSUs (shares)	387	0	0	0
Weighted average number of common and potential common shares	345,672	343,870	344,774	343,304
Diluted net loss per common share (USD per share)	$ 0.02	$ (1.75)	$ (1.58)	$ (2.25)
Antidilutive securities excluded from computation of earnings per share (shares)	22,600