Common Stock - Reserved for Future Issuance (Detail)	Dec. 31, 2014	Dec. 31, 2013
Common Stock Capital Shares Reserved For Future Issuance [Line Items]
Shares reserved for future issuance	2,928,474	10,136,128
Series A Convertible Preferred Stock [Member]
Common Stock Capital Shares Reserved For Future Issuance [Line Items]
Shares reserved for future issuance		7,125,982
Series B Convertible Preferred Stock [Member]
Common Stock Capital Shares Reserved For Future Issuance [Line Items]
Shares reserved for future issuance		1,134,462
Series A Preferred Stock Warrant [Member]
Common Stock Capital Shares Reserved For Future Issuance [Line Items]
Shares reserved for future issuance		30,708
Unvested Restricted Stock [Member]
Common Stock Capital Shares Reserved For Future Issuance [Line Items]
Shares reserved for future issuance	125,027	163,353
Options to Purchase Common Stock [Member]
Common Stock Capital Shares Reserved For Future Issuance [Line Items]
Shares reserved for future issuance	1,904,107	1,347,824
Common Stock Warrants [Member]
Common Stock Capital Shares Reserved For Future Issuance [Line Items]
Shares reserved for future issuance	899,340	333,799