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Subsequent events (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
	Oct. 19, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Oct. 26, 2021
Subsequent Event [Line Items]
Dividends declared per share (in usd per share)		$ 0.27	$ 0.26	$ 0.81	$ 0.78
Proceeds from revolving line of credit				$ 100,000	$ 20,000
Subsequent event
Subsequent Event [Line Items]
Dividends declared per share (in usd per share)	$ 0.27
Subsequent event \| Minimum
Subsequent Event [Line Items]
Current estimate of pre-tax charges						$ 8,000
Subsequent event \| Maximum
Subsequent Event [Line Items]
Current estimate of pre-tax charges						$ 9,000
Subsequent event \| Secured Revolving Loan Facility \| Credit Agreement
Subsequent Event [Line Items]
Proceeds from revolving line of credit	$ 200,000
Subsequent event \| Corporation Specializing In High Power Test And Measurement Applications
Subsequent Event [Line Items]
Total cash consideration	200,000
Cash acquired from acquisition	$ 3,000