Supplemental Cash Flow Information (Tables)

12 Months Ended

Dec. 31, 2017

Supplemental Cash Flow Information [Abstract]

Summary of Supplemental Cash Flow Information

The following table discloses supplemental cash flow information about cash paid for interest and income tax payments and refunds. Also disclosed is information about investing activities that affects recognized assets and liabilities but does not result in cash receipts or payments.

	Year ended December 31,
In thousands	2017		2016			2015
Supplemental cash flow information:
Cash paid for interest	$	281,058	$	316,116		$	301,743
Cash paid for income taxes	2		2			30
Cash received for income tax refunds	257		174			61,403
Non-cash investing activities:
Asset retirement obligation additions and revisions, net	14,685		(10,063		)	22,472