Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2019

Asset Retirement Obligation Disclosure [Abstract]

Summary of Changes in Asset Retirement Obligation Liability Balances

The components of the changes in the asset retirement obligation liabilities for the periods stated were as follows:

(Dollars in thousands)	Short-Term Portion			Long-Term Portion			Total
Balance at January 1, 2018	$	234		$	7,174		$	7,408
Accretion	(91		)	633			542
Amounts paid	(154		)	—			(154		)
Additions	—			55			55
Reductions	(185		)	(1,119		)	(1,304		)
Reclassifications	230			(230		)	—
Balance at December 31, 2018	34			6,513			6,547
Accretion	39			513			552
Amounts paid	(177		)	—			(177		)
Additions	—			32			32
Reductions	14			(817		)	(803		)
Reclassifications	180			(180		)	—
Balance at December 31, 2019	$	90		$	6,061		$	6,151