SUPPLEMENTAL BALANCE SHEET AND CASH FLOW INFORMATION (allowances for uncollectible accounts, inventories and supplies) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Allowances for uncollectible accounts
Balance, beginning of year	$ 3,639	$ 2,884	$ 2,828
Bad debt expense	5,213	3,622	3,208
Write-offs, net of recoveries	(3,867)	(2,867)	(3,152)
Balance, end of year	4,985	3,639	$ 2,884
Inventories and supplies
Raw materials	6,977	7,543
Semi-finished goods	7,368	7,273
Finished goods	21,982	27,608
Supplies	3,594	4,017
Inventories and supplies	$ 39,921	$ 46,441

The write-off of bad debts, net of recoveries of amounts that had previously been written off.

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- Definition

Amount of allowance for credit loss on accounts receivable, classified as current.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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- Definition

Carrying amount, net of valuation reserves and adjustments, as of the balance sheet date of merchandise or goods held by the company that are readily available for sale.

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Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer.

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Carrying amount, net of valuation reserves and adjustments, as of the balance sheet date of unprocessed items to be consumed in the manufacturing or production process.

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Carrying amount, net of valuation reserves and adjustments, as of the balance sheet date of products used directly or indirectly in the manufacturing or production process, which may or may not become part of the final product. May also include items used in the storage, presentation or transportation of physical goods.

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Carrying amount, net of reserves and adjustments, as of the balance sheet date of merchandise or goods which are partially completed. This inventory is generally comprised of raw materials, labor and factory overhead costs, which require further materials, labor and overhead to be converted into finished goods, and which generally require the use of estimates to determine percentage complete and pricing.

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Amount of expense (reversal of expense) for expected credit loss on accounts receivable.

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