SUPPLEMENTAL BALANCE SHEET AND CASH FLOW INFORMATION (trade accounts receivable) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Trade accounts receivable
Trade accounts receivable - gross		$ 202,077	$ 168,387
Allowance for uncollectible accounts		(4,130)	(6,428)	$ (4,985)
Trade accounts receivable - net	[1]	197,947	161,959
Unbilled receivables		47,420	21,319
Changes in allowances for uncollectible accounts
Balance, beginning of year		6,428	4,985	3,639
Bad debt expense		223	5,003	5,213
Write-offs and other		(2,521)	(3,560)	(3,867)
Balance, end of year		$ 4,130	$ 6,428	$ 4,985

[1] Includes unbilled receivables of $47,420 as of December 31, 2021 and $21,319 as of December 31, 2020.