Income taxes (Details) - USD ($)	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Income taxes
Income tax expense	$ 15,437,000	$ 6,760,000	$ 48,741,000	$ 28,800,000
Effective income tax rate	25.00%	21.00%	29.00%	23.00%
Recorded net income tax benefits no longer deductible					$ 6,228,000

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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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration