Accrued liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Accrued payroll and employee benefits	$ 33,981	$ 32,815
Short-term finance leases	16,545	16,542
Short-term operating leases	8,479	8,784
Accrued taxes	12,009	5,354
Warranty	7,419	5,536
Accrued rebates	8,382	9,895
Short-term derivative liability	331	0
Environmental obligation	83	718
Other miscellaneous accrued liabilities	10,205	9,195
Total accrued liabilities	$ 97,434	$ 88,839