Collaborations (Details)	1 Months Ended							3 Months Ended								8 Months Ended	12 Months Ended
	Apr. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Nov. 30, 2018 USD ($)	Jul. 31, 2017 USD ($)	Feb. 28, 2014 USD ($) $ / shares shares	Jul. 31, 2013 USD ($)	Jul. 31, 2010 target	Dec. 31, 2019 USD ($) shares	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) shares	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Jan. 31, 2014 USD ($)	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares	Jan. 01, 2018 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax								$ 18,000	$ 18,000	$ 18,000	$ 6,778,000	$ 18,000	$ 18,000	$ 18,000	$ 18,000		$ 6,832,000	$ 72,000
Common stock, shares issued (shares) | shares								21,018,663				8,818,019					21,018,663	8,818,019
Common stock value								$ 21,000				$ 9,000					$ 21,000	$ 9,000
Upfront payment received		$ 1,800,000	$ 2,500,000
Deferred revenue																			$ 77,000
Strategic Alliances and Collaborations
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax																	6,800,000	100,000
Sanofi
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of collaborative areas granted | target							4
Upfront payment received	$ 6,800,000	$ 6,800,000			$ 400,000													$ 2,500,000
Expected revenue through milestone payments			$ 6,800,000.0
Agreement period			24 months
Development Milestone Not Achievable								40,000,000									40,000,000
Sanofi | Private Placement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Common stock, shares issued (shares) | shares					108,648
Price per share (in dollars per share) | $ / shares					$ 92.04
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 | Development Commercialization And License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Initial upfront option payment					$ 2,500,000	$ 2,500,000
Deferred revenue creditable against future milestones				$ 1,250,000	$ 1,250,000												$ 1,250,000
Milestone payments, earned																$ 1,250,000
Sanofi | Minimum | United States
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Royalties based on percentage of net sales																	1000.00%
Sanofi | Minimum | Outside of the US
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Royalties based on percentage of net sales																	1000.00%
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 US
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Royalties based on percentage of net sales																	20.00%
Sanofi | Common Stock Purchase Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue								100,000									$ 100,000
Deferred revenue recognition period																	1 year
Sanofi | Development Milestones
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expected revenue through milestone payments			$ 40,000,000
Sanofi | Proof-of-Concept Trial
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expected revenue through milestone payments								38,800,000.0									$ 38,800,000.0
Sanofi | Clinical
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expected revenue through milestone payments								40,000,000.0									40,000,000.0
Sanofi | Regulatory and Commercialization Milestones
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expected revenue through milestone payments								$ 130,000,000.0									$ 130,000,000.0