Description of Business and Summary of Significant Accounting Policies - Additional Information (Detail)				1 Months Ended	3 Months Ended			12 Months Ended
	Mar. 26, 2020	Nov. 07, 2019 USD ($)	Jun. 25, 2019 $ / shares	Jul. 31, 2017 USD ($)	Mar. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Mar. 31, 2020 USD ($) Employee shares	Mar. 31, 2019 USD ($) shares	Mar. 31, 2018 USD ($) shares
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Reverse stock split								20:1 to 40:1
Cash and cash equivalents					$ 27,356,000			$ 27,356,000	$ 36,477,000
Accumulated deficit					$ (279,465,000)			(279,465,000)	(260,755,000)
Cash flow from operations								$ 14,882,000	$ 20,375,000
Issuance of common stock | shares					130,558,098			130,558,098	124,015,429
Gross proceeds from sale of common stock shares								$ 4,996,000	$ 13,327,000
Number of employees terminated | Employee								52
Percentage of workforce terminated								90.00%
Restricted cash					$ 0			$ 0	79,000
Inventory					0			$ 0
Inventory of raw materials, net of reserves									361,000
Inventory of work-in-process, net of reserves									0
Inventory of finished goods, net of reserves									129,000
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					0			0	525,000
Revenue recognized								525,000
Sale of inventory and associated assets								747,000	3,000
Revenue recognized under grants								2,196,000	3,091,000
Cost of revenue							$ 0	300,000	500,000
Inventory write-off							200,000	214,000	0
Dilutive effect									$ 0	$ 0
Common stock equivalents excluded from computing diluted net loss per share | shares									12,100,000	14,400,000
NIH Research Grants Two [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Revenue recognized under grants				$ 1,657,000
Other Income [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Sale of inventory and associated assets		$ 1,500,000						0
Product [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Product return revenue		$ 0						0
Grants [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Revenue recognized under grants								52,000	$ 587,000
Revenue unutilized remaining available balance								500,000
Grants [Member] | NIH Research Grants Two [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Revenue recognized under grants								52,000,000	587,000,000
Expiration Agreement [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Revenue related to expiration of an agreement								490,000
Research and Development Services [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Deferred revenue					0			0	$ 525,000
Employee Severance and Benefits Costs [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Restructuring charges								$ 2,700,000
Payments for restructuring					$ 100,000	$ 900,000	$ 1,700,000
At-The-Market Facility [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Issuance of common stock | shares					6,087,382			6,087,382
Gross proceeds from sale of common stock shares								$ 5,000,000
Minimum [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Minimum closing bid price | $ / shares			$ 1
Conversion ratio	20
Useful life of fixed assets, range								1 year
Maximum [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Conversion ratio	40
Restricted cash					$ 0			$ 0
Maturity of highly liquid investment								90 days
Useful life of fixed assets, range								7 years