Book overdrafts and cash pooling - Additional Information (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 145,283	$ 120,389
Outstanding A/P check
Cash and Cash Equivalents [Line Items]
Outstanding A/P checks	8,796	13,205
Outstanding payroll checks
Cash and Cash Equivalents [Line Items]
Outstanding A/P checks	38	114
Notional Pooling Arrangement
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 4,409	$ 2,562