Summary of significant accounting policies - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Total net sales	$ 64,527	$ 59,764
United States
Disaggregation of Revenue [Line Items]
Total net sales	57,897	53,780
International
Disaggregation of Revenue [Line Items]
Total net sales	$ 6,630	$ 5,984