Note 14 - Asset Retirement Obligation (Tables)

12 Months Ended

Dec. 31, 2021

Notes Tables

Schedule of Asset Retirement Obligations [Table Text Block]

	Year Ended December 31,
	2021		2020			2019
	(Dollars in thousands)
Balance at beginning of year	$	63,457	$	50,183		$	39,475
Revision in estimated cash flows		10,504		(165	)		(335	)
Liabilities incurred and acquired		6,953		10,207			8,334
Accretion expense		3,977		3,232			2,709
Balance at end of year	$	84,891	$	63,457		$	50,183