Income taxes (Details) - USD ($)	3 Months Ended	6 Months Ended	12 Months Ended
Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Income taxes
Income tax expense	$ 27,656,000		$ 15,401,000	$ 33,304,000	$ 22,040,000
Effective income tax rate	34.00%		22.00%	30.00%	23.00%
Recorded net income tax benefits denied		$ 1,072,000				$ 6,228,000

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

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