Description of Business and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Cash and cash equivalents	$ 36,477,000	$ 43,726,000
Accumulated deficit	(260,755,000)	(234,120,000)
Cash flow from operations	$ 20,375,000	$ 28,857,000
Issuance of common stock	124,015,429	111,032,957
Gross proceeds from sale of common stock shares	$ 13,327,000	$ 9,381,000
Foreign currency translation adjustment	0	(1,000)
Cumulative foreign currency translation losses	0	(11,000)
Restricted cash	79,000	127,000
Inventory of raw materials, net of reserves	361,000	578,000
Inventory of work-in-process, net of reserves	0	26,000
Inventory of finished goods, net of reserves	$ 129,000	238,000
Estimated useful life of the fixed assets	The estimated useful lives of the fixed assets range between one and seven years.
Impairment of long-lived assets	$ 0
Deferred revenue	525,000	668,000
Revenue recognized		178,000,000
Revenue recognized under grants	3,091,000	4,603,000
Cost of revenue	500,000	1,000,000
Dilutive effect	$ 0	$ 0
Common stock equivalents excluded from computing diluted net loss per share	14,400,000	12,600,000
Grants [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Revenue recognized under grants	$ 587,000	$ 554,000
NIH Research Grants Two [Member] | Grants [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Revenue recognized under grants	587,000,000	554,000,000
Research and Development Services [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Deferred revenue	$ 525,000	$ 687,000
At-The-Market Facility [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Issuance of common stock	11,631,803
Gross proceeds from sale of common stock shares	$ 13,200,000
Maximum [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Restricted cash	$ 100,000
Maturity of highly liquid investment	90 days
Useful life of fixed assets, range	7 years
Minimum [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Useful life of fixed assets, range	1 year