Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)			3 Months Ended		9 Months Ended		12 Months Ended
	Aug. 17, 2015	Jul. 02, 2015	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Jun. 26, 2015
Accounting Policies [Line Items]
Maximum maturity days for cash equivalents					90 days
Restricted cash			$ 139,000		$ 139,000		$ 139,000
Fair value, assets transfers from Level 1 to Level 2 measurement			0	$ 0	0	$ 0
Fair value, assets transfers from Level 2 to Level 1 measurement			0	0	0	0
Fair Value, assets transfers into (out of) Level 3 measurement					0		0
Deferred offering costs							1,684,000
Reclassification of deferred offering costs to additional paid in capital		$ 3,748,000
Impairment losses on long lived assets					$ 0
Minimum percentage of likelihood of tax benefit being realized upon settlement					50.00%
Revenue			0	$ 0	$ 0	$ 0
Laboratory Equipment [Member]
Accounting Policies [Line Items]
Useful life of asset					5 years
Computer Equipment [Member]
Accounting Policies [Line Items]
Useful life of asset					3 years
Furniture and Office Equipment [Member]
Accounting Policies [Line Items]
Useful life of asset					3 years
Common Stock [Member]
Accounting Policies [Line Items]
Warrants exercise price per share	$ 1.78
Proceeds from exercise of warrant	$ 164,000
Initial Public Offering ("IPO") [Member]
Accounting Policies [Line Items]
Deferred offering costs			$ 0		$ 0		1,684,000
Initial Public Offering ("IPO") [Member] | Common Stock [Member]
Accounting Policies [Line Items]
Public offering price per share		$ 18.00						$ 18.00
Fair Value, Inputs, Level 3 [Member]
Accounting Policies [Line Items]
Liability for preferred stock warrant							$ 1,582,000