Comprehensive income (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 1,176,350	$ 1,238,358
Current-period other comprehensive (loss) income	82	5,153
Reclassified from accumulated OCI into income	(2,809)	(4,310)
Income tax expense (benefit)	68	(58)
Ending Balance	1,269,639	1,174,574
Currency translation adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(25,831)	(22,485)
Current-period other comprehensive (loss) income	(1,975)	(802)
Reclassified from accumulated OCI into income	0	0
Income tax expense (benefit)	0	0
Ending Balance	(27,806)	(23,287)
Investments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(85)	(1,308)
Current-period other comprehensive (loss) income	(154)	1,913
Reclassified from accumulated OCI into income	0	0
Income tax expense (benefit)	(56)	8
Ending Balance	(183)	597
Derivative instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	4,846
Current-period other comprehensive (loss) income	2,211
Reclassified from accumulated OCI into income	(2,809)
Income tax expense (benefit)	124
Ending Balance	4,124
Derivative instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance		6,862
Current-period other comprehensive (loss) income		4,042
Reclassified from accumulated OCI into income		(4,310)
Income tax expense (benefit)		(66)
Ending Balance		6,660
Accumulated other comprehensive income/(loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(21,070)	(16,931)
Ending Balance	$ (23,865)	$ (16,030)

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount before tax and reclassification adjustments of other comprehensive income (loss) attributable to parent.

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