Net Loss Per Common Share - Potential Common Stock Equivalents Excluded from Calculation of Diluted Net Loss Per Common Share (Detail) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	2,564,383	2,654,541	3,127,954
Outstanding Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	1,267,329	1,684,783	2,792,021
Unvested Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	1,297,054	969,758	335,933