Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2017

Accounting Policies [Abstract]

Schedule of Earnings Per Share

	Three Months					Nine Months
	Ended September 30,					Ended September 30,
	2017			2016		2017		2016
	(Share amounts in 000's)
Net income (loss)	$	(327,727	)	$	98,407	$	81,611	$	90,577
Weighted average common shares outstanding - basic		196,331			80,003		152,864		79,991
Effect of dilutive instruments		—			381		204		370
Weighted average common shares outstanding - diluted		196,331			80,384		153,068		80,361
Net income (loss) per common share - basic	$	(1.67	)	$	1.23	$	0.53	$	1.13
Net income (loss) per common share - diluted	$	(1.67	)	$	1.22	$	0.53	$	1.13
Number of shares not included in dilutive earnings per    share that would have been anti-dilutive because the    exercise price was greater than the average market    price of the common shares		—			262		—		756