Commitments and Contingencies (Details)			1 Months Ended				3 Months Ended				44 Months Ended	53 Months Ended	63 Months Ended
	Aug. 05, 2016 item $ / shares shares	Nov. 13, 2015 USD ($) patent shares	Aug. 31, 2019	Nov. 30, 2018 manufacturing_suite	Aug. 31, 2016 USD ($) shares	Nov. 30, 2015 USD ($) shares	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2020 shares	Mar. 31, 2020 USD ($)	Mar. 31, 2020 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Stock-based compensation expense							$ 1,669,000	$ 1,729,000
License Agreement | Restricted Common Stock
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate fair value		$ 200,000
License Agreement | Broad
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of patent families | patent		12
Non-refundable license fee paid		$ 100,000
Shares granted (in shares) | shares					120,000	60,000
Aggregate fair value					$ 200,000	$ 100,000
Reimbursement amount		600,000				600,000
License Agreement | Broad | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Developmental milestone payments to be paid on achievements		12,600,000				12,600,000
Payments upon achievement of specified sales milestones and tiered royalties on net sales		$ 97,500,000				$ 97,500,000
Developmental and commercial milestones achieved to date under collaborative arrangement												$ 0	$ 0
License Agreement | Broad | Restricted Common Stock
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Shares granted (in shares) | shares	120,000	60,000
Shares expired (in shares) | shares											120,000
Stock-based compensation expense							$ 0	$ 0
License Agreement | DFCI
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Term of agreement	3 years
Number of specific milestones with contingent repurchase option | item	3
Percentage of shares with contingent repurchase option expired on achievement of specific criteria								0.33	0.33	0.33
License Agreement | DFCI | Restricted Common Stock
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Shares granted (in shares) | shares	120,000	60,000
Shares granted with contingent repurchase option (in shares) | shares	120,000
Original purchase price of shares (in dollars per share) | $ / shares	$ 0
License Agreement | MGH | Restricted Common Stock
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Shares granted (in shares) | shares		60,000
Vendor | Manufacturing Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of manufacturing suites | manufacturing_suite				2
Term of agreement				5 years
Notice period for termination of agreement				3 months
NKI | Manufacturing Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Term of agreement			3 years
Notice period for termination of agreement			3 months
Additional agreement term			6 months