Income taxes (Deferred Tax Assets) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017
Current deferred tax assets
Net operating loss carryforwards	$ 40,465	$ 36,427
Research and development and other credit carryforwards	11,761	8,614
Stock-based compensation	6,389	6,942
Reserves and allowances	3,181	3,266
Fixed assets and intangibles	378	(3,688)
Net non-current deferred tax assets	62,174	51,561
Valuation allowance	(62,174)	(2,934)
Total	$ 0	$ 48,627