Accrued expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accrued expenses
Accrued savings offers	$ 11,289	$ 7,168
Accrued rebates	7,762	4,008
Accrued customer returns	5,157	2,711
Accrued payroll and benefits	4,555	2,534
Accrued wholesaler fees	4,249	2,345
Other accrued expenses	2,806	2,178
Total accrued expenses	$ 35,818	$ 20,944