Significant Accounting Policies (Reconciliation of Weighted Average Shares Table) (Details 2) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator
Net income (loss) - basic	$ 322,698	$ 163,152	$ (976,177)
Interest on convertible senior notes	539	49	0
Net income (loss) - diluted	$ 323,237	$ 163,201	$ (976,177)
Denominator
Weighted average common shares outstanding – basic	432,483	390,928	373,859
Restricted stock, stock options, SARs and performance-based equity awards	6,500	2,242	0
Convertible senior notes	17,186	2,751	0
Weighted average common shares outstanding – diluted	456,169	395,921	373,859