Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2018

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)	2018			2017
Balance at beginning of year	$	109,653		$	101,106
Accretion expense		5,074			4,768
Liabilities incurred and liabilities assumed in business combinations		4,692			7,940
Liabilities settled		(2,821	)		(309	)
Revisions in estimated cash flows		5,206			(3,852	)
Balance at end of year	$	121,804		$	109,653

Schedule of Contractual Purchase Commitments

The Company’s contractual purchase commitments as of December 31, 2018 are as follows:

(add 000)

2019	$	181,768
2020		14,177
2021		6,264
2022		3,689
2023		1,931
Thereafter		17,195
Total	$	225,024