Income taxes (Deferred Tax Assets) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Mar. 31, 2015
Current deferred tax assets
Net operating loss carryforwards	$ 2,739	$ 2,179
Inventory valuation	14	14
Reserves and allowances	2,740	2,394
Net current deferred tax assets	5,493	4,587
Net operating loss carryforwards	38,449	44,228
Research and development and other credit carryforwards	7,106	5,414
Stock-based compensation	5,577	3,164
Fixed assets and intangibles	(6,160)	(4,869)
Net non-current deferred tax assets	44,972	47,937
Valuation allowance	(3,760)	(4,901)
Total	$ 46,705	$ 47,623