Income taxes (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Taxes
Income tax expense (benefit)	$ 1,325,000	$ (3,805,000)	$ 1,655,000	$ (3,105,000)
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	28.90%	43.70%	29.20%	49.00%
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount		$ 1,100,000		$ 1,100,000