Commitments and Contingencies - Additional Information (Detail)	1 Months Ended							3 Months Ended	12 Months Ended
	Nov. 30, 2016 USD ($)	May 31, 2016 USD ($)	Jan. 31, 2016 USD ($)	Sep. 30, 2015 USD ($)	Mar. 31, 2015	Nov. 30, 2014 USD ($)	Mar. 31, 2009 USD ($)	Mar. 31, 2017 USD ($) Milestone	Dec. 31, 2016 USD ($)
Other Commitments [Line Items]
Tenant improvement allowance received				$ 300,000
Restricted cash as collateral with financial institution								$ 225,000	$ 225,000
Claims paid to date related to indemnification issues								0
Accruals or expenses related to indemnification issues								$ 0	0
The Trustees of the University of Pennsylvania [Member]
Other Commitments [Line Items]
Percentage of ownership interest issued as consideration for license agreement								24.50%
Accrued expenses								$ 100,000	200,000
GlaxoSmithKline LLC [Member]
Other Commitments [Line Items]
Percentage of ownership interest issued as consideration for license agreement							19.90%
Accrued expenses								$ 200,000	400,000
Number of milestone | Milestone								0
Milestone payment obligation							$ 1,500,000	$ 0
Regents of the University of Minnesota [Member]
Other Commitments [Line Items]
Number of milestone | Milestone								0
Milestone payments								$ 0
Regents of the University of Minnesota [Member] | Maximum [Member]
Other Commitments [Line Items]
Up-front fee paid and patent maintenance expenses reimbursed						$ 100,000
Up-front fee paid	$ 100,000
Amounts due under agreement								$ 100,000	$ 100,000
Regents of the University of Minnesota [Member] | Annual License Maintenance Fee [Member] | Maximum [Member]
Other Commitments [Line Items]
Contractual obligation						100,000
Regents of the University of Minnesota [Member] | Royalties And Sublicense Fees [Member] | Maximum [Member]
Other Commitments [Line Items]
Contractual obligation						$ 100,000
Rockville, Maryland [Member]
Other Commitments [Line Items]
Lease period			7 years 6 months	5 years	5 years 6 months
Lease expiration date			Sep. 30, 2023	Mar. 31, 2021	Sep. 30, 2020
Options to extend the lease					6 years
Lease commenced date			2016-02		2015-04
Lease term								Extend the term of the lease for its existing space to October 2020.
Tenant improvement allowance received			$ 700,000
Monthly lease payments commencement period			2016-09
New York, New York [Member]
Other Commitments [Line Items]
Lease expiration date		Oct. 31, 2020
Lease commenced date		2016-07
Monthly lease payments commencement period		2016-10
Lease expiration term		51 months
Letters of credit		$ 200,000