Asset Retirement Obligation (Tables)

12 Months Ended

Dec. 31, 2017

Asset Retirement Obligation Disclosure [Abstract]

Information Related to Asset Retirement Obligations

The following table reflects information related to our asset retirement obligations:

Balance at December 31, 2015	$	206,234
Additions to asset retirement obligations		5,008
Accretion expense		4,272
Liabilities settled		(4,625	)
Balance at December 31, 2016	$	210,889
Additions to asset retirement obligations		4,003
Accretion expense		4,236
Liabilities settled		(4,039	)
Balance at December 31, 2017	$	215,089