Stockholders' Equity - Schedule of Number of Shares of Common Stock Reserved for Future Issuance (Detail) - shares	Jun. 30, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Common stock shares reserved for future issuance	6,748,762	5,892,594
Unvested Restricted Stock [Member]
Class of Stock [Line Items]
Common stock shares reserved for future issuance	956,247	1,164,040
Common Stock Options Outstanding [Member]
Class of Stock [Line Items]
Common stock shares reserved for future issuance	385,974	666,717
Shares Available for Issuance Under the 2013 Stock Option and Incentive Plan [Member]
Class of Stock [Line Items]
Common stock shares reserved for future issuance	4,618,038	3,273,334
Shares Available for Issuance Under the 2013 Employee Stock Purchase Plan [Member]
Class of Stock [Line Items]
Common stock shares reserved for future issuance	788,503	788,503