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Stock Option Plans - Schedule of Stock-based Compensation Expense (Detail) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]      
Stock-based compensation expense $ 885us-gaap_AllocatedShareBasedCompensationExpense $ 622us-gaap_AllocatedShareBasedCompensationExpense $ 529us-gaap_AllocatedShareBasedCompensationExpense
Research and Development [Member]      
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]      
Stock-based compensation expense 317us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_ResearchAndDevelopmentExpenseMember
284us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_ResearchAndDevelopmentExpenseMember
187us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_ResearchAndDevelopmentExpenseMember
General and Administrative [Member]      
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]      
Stock-based compensation expense $ 568us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_GeneralAndAdministrativeExpenseMember
$ 338us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_GeneralAndAdministrativeExpenseMember
$ 342us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_GeneralAndAdministrativeExpenseMember