Commitments and Contingencies - Additional Information (Detail)		1 Months Ended	3 Months Ended		9 Months Ended
	Nov. 02, 2015 USD ($) ft² $ / ft²	Jun. 30, 2015 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)
Commitments and Contingencies [Line Items]
Operating leases, rent expense			$ 171,000	$ 71,000	$ 563,000	$ 157,000
ARE-MA Region No.20 LLC [Member] | Laboratory and Office Facility [Member] | Subsequent Event [Member]
Commitments and Contingencies [Line Items]
Operating lease, area of property leased | ft²	17,500
Operating lease, term	5 years
Operating lease, annual rent	$ 400,000
Operating lease, annual increase in rent per square foot | $ / ft²	1.00
Operating lease, tenant improvement allowance per rentable square foot | $ / ft²	35.00
Eunice Kennedy Shriver National Institute of Child Health and Human Development [Member]
Commitments and Contingencies [Line Items]
Research and development agreement period		3 years
Noncancelable research funding payments minimum amount committed		$ 244,000
Research funding potential aggregate amount		$ 732,000