Income taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Taxes
Income tax expense (benefit)	$ (3,805)	$ 1,850	$ (3,105)	$ 2,400
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	43.70%	28.10%	49.00%	28.20%
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount	$ 1,100		$ 1,100