Annual report pursuant to Section 13 and 15(d)

Common Stock - Summary of Share-Based Compensation Expense (Detail)

v2.4.1.9
Common Stock - Summary of Share-Based Compensation Expense (Detail) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]      
Total stock-based compensation $ 3,860us-gaap_ShareBasedCompensation $ 2,834us-gaap_ShareBasedCompensation $ 2,175us-gaap_ShareBasedCompensation
Research and development [Member]      
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]      
Total stock-based compensation 1,893us-gaap_ShareBasedCompensation
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_ResearchAndDevelopmentExpenseMember 		1,296us-gaap_ShareBasedCompensation
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_ResearchAndDevelopmentExpenseMember 		899us-gaap_ShareBasedCompensation
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_ResearchAndDevelopmentExpenseMember
General and administrative [Member]      
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]      
Total stock-based compensation $ 1,967us-gaap_ShareBasedCompensation
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_GeneralAndAdministrativeExpenseMember 		$ 1,538us-gaap_ShareBasedCompensation
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_GeneralAndAdministrativeExpenseMember 		$ 1,276us-gaap_ShareBasedCompensation
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_GeneralAndAdministrativeExpenseMember