Supplemental balance sheet and cash flow information (trade accounts receivable, allowance for credit losses) (Details) - USD ($) $ in Thousands		6 Months Ended
		Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Trade accounts receivable
Trade accounts receivable - gross		$ 190,844		$ 202,077
Allowance for credit losses		(4,253)		(4,130)
Trade accounts receivable - net	[1]	186,591		197,947
Unbilled receivables		52,647		$ 47,420
Changes in allowance for credit losses
Balance, beginning of year		4,130	$ 6,428
Bad debt expense (benefit)		1,449	(1,696)
Write-offs and other		(1,326)	(1,704)
Balance, end of period		$ 4,253	$ 3,028

[1] Includes unbilled receivables of $52,647 as of June 30, 2022 and $47,420 as of December 31, 2021.