Income taxes (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Taxes
Income tax expense (benefit)	$ 1,375,000	$ 1,130,000	$ 3,030,000	$ (1,975,000)
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	28.50%	627.80%	28.90%	32.10%
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount		$ 400,000		$ 1,500,000