Income taxes (Details) - USD ($)	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Income taxes
Income tax expense	$ 8,419,000	$ 5,648,000
Effective income tax rate	23.00%	20.00%

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Name:	us-gaap_IncomeTaxExpenseBenefit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration