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Total Compensation Cost from Share-Based Payments (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 [Line Items]      
Stock-based compensation cost $ 32,403us-gaap_ShareBasedCompensation $ 35,421us-gaap_ShareBasedCompensation $ 20,341us-gaap_ShareBasedCompensation
Research and development expense      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation cost 13,856us-gaap_ShareBasedCompensation
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_ResearchAndDevelopmentExpenseMember		 15,150us-gaap_ShareBasedCompensation
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_ResearchAndDevelopmentExpenseMember		 9,846us-gaap_ShareBasedCompensation
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_ResearchAndDevelopmentExpenseMember
Selling, general and administrative expense      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation cost 18,547us-gaap_ShareBasedCompensation
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SellingGeneralAndAdministrativeExpensesMember		 20,271us-gaap_ShareBasedCompensation
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SellingGeneralAndAdministrativeExpensesMember		 10,495us-gaap_ShareBasedCompensation
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SellingGeneralAndAdministrativeExpensesMember
Stock options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation cost 16,608us-gaap_ShareBasedCompensation
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember		 16,364us-gaap_ShareBasedCompensation
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember		 10,626us-gaap_ShareBasedCompensation
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Stock and stock units      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation cost 15,346us-gaap_ShareBasedCompensation
/ us-gaap_AwardTypeAxis
= aria_StockAndStockUnitsMember		 18,458us-gaap_ShareBasedCompensation
/ us-gaap_AwardTypeAxis
= aria_StockAndStockUnitsMember		 9,467us-gaap_ShareBasedCompensation
/ us-gaap_AwardTypeAxis
= aria_StockAndStockUnitsMember
Purchases of common stock at a discount      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation cost $ 449us-gaap_ShareBasedCompensation
/ us-gaap_PlanNameAxis
= aria_EmployeeStockPurchasePlansMember		 $ 599us-gaap_ShareBasedCompensation
/ us-gaap_PlanNameAxis
= aria_EmployeeStockPurchasePlansMember		 $ 248us-gaap_ShareBasedCompensation
/ us-gaap_PlanNameAxis
= aria_EmployeeStockPurchasePlansMember