Summary of significant accounting policies - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Total net sales	$ 72,350	$ 67,615	$ 136,877	$ 127,379
United States
Disaggregation of Revenue [Line Items]
Total net sales	63,655	59,731	121,552	113,511
International
Disaggregation of Revenue [Line Items]
Total net sales	$ 8,695	$ 7,884	$ 15,325	$ 13,868