Significant Accounting Policies - Schedule of Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Earnings Per Share Reconciliation [Abstract]
Net income (loss)	$ 18,563	$ (327,727)	$ 45,502	$ 81,611	$ 177,140
Weighted average common shares outstanding - basic	197,054	196,331	196,888	152,864
Effect of dilutive instruments	1		400	204
Weighted average common shares outstanding - diluted	197,055	196,331	197,288	153,068
Net income (loss) per common share - basic	$ 0.09	$ (1.67)	$ 0.23	$ 0.53
Net income (loss) per common share - fully diluted	$ 0.09	$ (1.67)	$ 0.23	$ 0.53