Concentrations and credit risk (Tables)

12 Months Ended

Mar. 31, 2019

Accounting Policies [Abstract]

Net sales to customers

The net revenue representing at least 10% of total net revenue are as follows:

	Year Ended March 31,
	2017				2018				2019
	$ in thousands		%		$ in thousands		%		$ in thousands		%
Customer A		2,729		14		3,579		31		3,715		37
Customer C		2,435		13		1,599		14		1,225		12
Customer B		1,563		8		1,662		14		1,027		10
Customer E		1,061		6		1,050		9		996		10
Customer D *		8,472		45		1,115		10		21		—
		16,260		86		9,005		78		6,984		69

The following customers had balances of at least 10% of the total trade receivables at the respective balance sheet dates set forth below:

	March 31,
	2018				2019
	$ in thousands		%		$ in thousands		%
Customer B		—		—		191		32
Customer C		200		25		136		23
Customer A		234		30		127		21
Customer E		113		14		—		—
				69				76