Collaborations (Detail)	1 Months Ended						3 Months Ended		8 Months Ended
	Apr. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Nov. 30, 2018 USD ($)	Feb. 28, 2014 USD ($) $ / shares shares	Jul. 31, 2013 USD ($)	Jul. 31, 2012 target	Mar. 31, 2020 USD ($) shares	Mar. 31, 2019 USD ($)	Jan. 31, 2014 USD ($)	Dec. 31, 2019 USD ($) shares
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenues (less than)							$ 6,000	$ 6,778,000
Common stock, shares issued (shares) | shares							27,608,783			21,018,663
Common stock value							$ 22,000			$ 21,000
Upfront payment received		$ 1,800,000	$ 2,500,000
Revenue under collaborations
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenues (less than)							100,000	6,800,000
Sanofi
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of collaborative areas granted | target						4
Upfront payment non-creditable portion recognized								$ 2,500,000
Deferred revenue				$ 400,000
Potential revenue through milestone payments			$ 6,800,000.0
Agreement period			24 months
Upfront payment received	$ 2,500,000	$ 1,800,000	$ 2,500,000
Development milestone not achievable							$ 40,000,000
Sanofi | Private Placement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Common stock, shares issued (shares) | shares				1,303,780
Price per share (in dollars per share) | $ / shares				$ 7.67
Common stock value				$ 10,000,000
Restriction period in which Alliances could not sell, transfer, make any short sale of, or grant any option for the sale of any common stock				12 months
Sanofi | Minimum | United States
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Royalties based on percentage of net sales							10.00%
Sanofi | Minimum | Outside of the United States
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Royalties based on percentage of net sales							10.00%
Sanofi | Maximum | United States
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Royalties based on percentage of net sales							20.00%
Sanofi | Maximum | Outside of the United States
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Royalties based on percentage of net sales							20.00%
Sanofi | Development Commercialization And License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Initial upfront option payment					$ 2,500,000
Deferred revenue creditable against future milestones				$ 1,250,000	$ 1,250,000		$ 1,250,000
Upfront payment non-creditable portion recognized									$ 1,250,000
Sanofi | Proof-of-Concept Trial
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Potential revenue through milestone payments							38,800,000.0
Sanofi | Regulatory and Commercialization Milestones
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Potential revenue through milestone payments							130,000,000.0
Sanofi | Clinical
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Potential revenue through milestone payments							$ 40,000,000.0
Sanofi | Development Milestones
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Potential revenue through milestone payments			$ 40,000,000