Stockholders' Equity - Schedule of Number of Shares of Common Stock Reserved for Future Issuance (Detail) - shares	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2013
Class of Stock [Line Items]
Common stock shares reserved for future issuance	5,892,594	5,750,917
Unvested Restricted Stock [Member]
Class of Stock [Line Items]
Common stock shares reserved for future issuance	1,164,040	1,297,054
Common Stock Options Outstanding [Member]
Class of Stock [Line Items]
Common stock shares reserved for future issuance	666,717	1,267,329
Shares Available for Issuance Under the 2013 Stock Plan [Member]
Class of Stock [Line Items]
Common stock shares reserved for future issuance	3,273,334	2,398,031
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
Shares Available for Issuance Under the 2013 Employee Stock Purchase Plan [Member] | Common Stock Options Outstanding [Member]
Class of Stock [Line Items]
Common stock shares reserved for future issuance			788,503