Other comprehensive income (accumulated other comprehensive loss) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2022 USD ($)
Postretirement benefit plans [Member]
Accumulated other comprehensive loss [Line Items]
Balance, December 31, 2021	$ (15,431)
Other comprehensive (loss) income before reclassifications	0
Amounts reclassified from accumulated other comprehensive loss	(155)
Net current-period other comprehensive (loss) income	(155)
Balance, September 30, 2022	(15,586)
Net unrealized loss on debt securities [Member]
Accumulated other comprehensive loss [Line Items]
Balance, December 31, 2021	(344)
Other comprehensive (loss) income before reclassifications	(566)	[1]
Amounts reclassified from accumulated other comprehensive loss	6
Net current-period other comprehensive (loss) income	(560)
Balance, September 30, 2022	(904)
Unrealized loss on debt securities arising during the period, tax benefit	197
Net unrealized loss on cash flow hedge [Member]
Accumulated other comprehensive loss [Line Items]
Balance, December 31, 2021	(2,261)
Other comprehensive (loss) income before reclassifications	4,712	[2]
Amounts reclassified from accumulated other comprehensive loss	303
Net current-period other comprehensive (loss) income	5,015
Balance, September 30, 2022	2,754
Unrealized gain on cash flow hedge arising during the period, tax expense	1,701
Currency translation adjustment [Member]
Accumulated other comprehensive loss [Line Items]
Balance, December 31, 2021	(13,456)
Other comprehensive (loss) income before reclassifications	(6,006)
Amounts reclassified from accumulated other comprehensive loss	5,550
Net current-period other comprehensive (loss) income	(456)
Balance, September 30, 2022	(13,912)
Accumulated other comprehensive loss [Member]
Accumulated other comprehensive loss [Line Items]
Balance, December 31, 2021	(31,492)
Other comprehensive (loss) income before reclassifications	(1,860)
Amounts reclassified from accumulated other comprehensive loss	5,704
Net current-period other comprehensive (loss) income	3,844
Balance, September 30, 2022	$ (27,648)

[1] Other comprehensive loss before reclassifications is net of an income tax benefit of $197.

[2] Other comprehensive income before reclassifications is net of income tax expense of $1,701.