Supplemental balance sheet and cash flow information (inventories and supplies) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Inventories and supplies
Raw materials	$ 6,736		$ 5,316
Semi-finished goods	7,004		6,708
Finished goods	22,677		21,995
Supplies	6,525		6,041
Reserves for excess and obsolete items	(5,437)	$ (5,456)	(5,132)
Inventories and supplies	37,505		$ 34,928
Changes in reserves for excess and obsolete items
Balance, beginning of year	5,132	11,748
Balance, end of period	5,437	5,456
Reserves for excess and obsolete items
Changes in reserves for excess and obsolete items
Amounts charged to expense	1,516	2,151
Write-offs and other	$ (1,211)	$ (8,443)