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Stock-Based Compensation Expense Included in Statement of Operations (Detail) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock-based compensation $ 1,093us-gaap_ShareBasedCompensation $ 1,223us-gaap_ShareBasedCompensation
Research and Development Expense    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock-based compensation 295us-gaap_ShareBasedCompensation
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_ResearchAndDevelopmentExpenseMember		 376us-gaap_ShareBasedCompensation
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_ResearchAndDevelopmentExpenseMember
General and Administrative Expense    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock-based compensation $ 798us-gaap_ShareBasedCompensation
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_GeneralAndAdministrativeExpenseMember		 $ 847us-gaap_ShareBasedCompensation
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_GeneralAndAdministrativeExpenseMember