Note 14 - Asset Retirement Obligation (Tables)

12 Months Ended

Dec. 31, 2019

Notes Tables

Schedule of Asset Retirement Obligations [Table Text Block]

	Year Ended December 31,
	2019			2018
	(Dollars in thousands)
Balance at beginning of year	$	39,475		$	27,110
Revision in estimated cash flows		(335	)		(258	)
Liabilities incurred and acquired		8,334			10,149
Accretion expense		2,709			2,474
Balance at end of year	$	50,183		$	39,475