Significant Accounting Policies (Reconciliation of Weighted Average Shares Table) (Details 2) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator
Net income (loss) - basic	$ 163,152	$ (976,177)	$ (4,385,448)
Interest on convertible senior notes	49	0	0
Net income (loss) - diluted	$ 163,201	$ (976,177)	$ (4,385,448)
Denominator
Weighted average common shares outstanding – basic	390,928	373,859	348,802
Restricted stock, stock options, SARs and performance-based equity awards	2,242	0	0
Convertible senior notes	2,751	0	0
Weighted average common shares outstanding – diluted	395,921	373,859	348,802