Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2014

Commitments And Contingencies Disclosure [Abstract]

Schedule of Changes in Asset Retirement Obligations

The following shows the changes in the asset retirement obligations:

years ended December 31:

(add 000)	2014			2013
Balance at beginning of year	$	48,727		$	46,173
Accretion expense		2,818			2,777
Liabilities incurred and assumed in business combinations		20,984			2,240
Liabilities settled		(2,061	)		—
Revisions in estimated cash flows		(46	)		(2,463	)
Balance at end of year	$	70,422		$	48,727

Schedule of Contractual Purchase Commitments

The Corporation’s contractual purchase commitments as of December 31, 2014 are as follows:

(add 000)

2015	$	171,367
2016		38,400
2017		4,302
2018		826
2019		826
Thereafter		4,821
Total	$	220,542