SUPPLEMENTAL BALANCE SHEET AND CASH FLOW INFORMATION (trade accounts receivable) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Trade accounts receivable
Trade accounts receivable - gross	$ 168,406	$ 177,501
Allowances for uncollectible accounts	(4,985)	(3,639)	$ (2,884)	$ (2,828)
Trade accounts receivable - net	$ 163,421	$ 173,862

Amount, after allowance for credit loss, of right to consideration from customer for product sold and service rendered in normal course of business, classified as current.

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Name:	us-gaap_AccountsReceivableNetCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant