Other comprehensive income (accumulated other comprehensive loss) (Details) $ in Thousands	6 Months Ended
	Jun. 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	(104)
Net current-period other comprehensive (loss) income	(104)
Balance, June 30, 2022	(15,535)
Net unrealized loss on debt securities [Member]
Accumulated other comprehensive loss [Line Items]
Balance, December 31, 2021	(344)
Other comprehensive (loss) income before reclassifications	(562)	[1]
Amounts reclassified from accumulated other comprehensive loss	6
Net current-period other comprehensive (loss) income	(556)
Balance, June 30, 2022	(900)
Unrealized loss on debt securities arising during the period, tax benefit	195
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	3,075	[2]
Amounts reclassified from accumulated other comprehensive loss	341
Net current-period other comprehensive (loss) income	3,416
Balance, June 30, 2022	1,155
Unrealized gain on cash flow hedge arising during the period, tax expense	1,111
Currency translation adjustment [Member]
Accumulated other comprehensive loss [Line Items]
Balance, December 31, 2021	(13,456)
Other comprehensive (loss) income before reclassifications	(1,768)
Amounts reclassified from accumulated other comprehensive loss	5,550
Net current-period other comprehensive (loss) income	3,782
Balance, June 30, 2022	(9,674)
Accumulated other comprehensive loss [Member]
Accumulated other comprehensive loss [Line Items]
Balance, December 31, 2021	(31,492)
Other comprehensive (loss) income before reclassifications	745
Amounts reclassified from accumulated other comprehensive loss	5,793
Net current-period other comprehensive (loss) income	6,538
Balance, June 30, 2022	$ (24,954)

[1] Other comprehensive loss before reclassifications is net of an income tax benefit of $195.

[2] Other comprehensive income before reclassifications is net of income tax expense of $1,111.