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Income Tax - Additional Information (Detail) (USD $)
 3 Months Ended 12 Months Ended
Dec. 31, 2013
Sep. 30, 2013
Jun. 30, 2013
Mar. 31, 2013
Dec. 31, 2012
Sep. 30, 2012
Jun. 30, 2012
Mar. 31, 2012
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Income Tax Disclosure [Line Items]                      
Increase (Decrease) in valuation allowance                 $ 8,500,000 $ (800,000) $ 2,000,000
Federal statutory income tax rate                 34.00%    
Undistributed earnings, federal statutory income taxes                 (14,661,000) (5,329,000) (5,725,000)
Net loss (5,860,000) (20,501,000) (6,724,000) (10,252,000) (1,716,000) (3,460,000) (1,907,000) (8,834,000) (43,337,000) (15,917,000) (16,982,000)
Research and development tax credit carryforwards 32,100,000       30,800,000       32,100,000 30,800,000  
Internal Revenue Service (IRS)
                      
Income Tax Disclosure [Line Items]                      
Net operating loss carryforwards 381,700,000               381,700,000    
Research and development tax credit carryforwards 21,600,000               21,600,000    
Internal Revenue Service (IRS) | Minimum
                      
Income Tax Disclosure [Line Items]                      
Net operating loss carryforwards, expiration year                 2018    
Research and development tax credit carryforwards, expiration year                 2018    
Internal Revenue Service (IRS) | Maximum
                      
Income Tax Disclosure [Line Items]                      
Net operating loss carryforwards, expiration year                 2033    
Research and development tax credit carryforwards, expiration year                 2033    
State and Local Jurisdiction
                      
Income Tax Disclosure [Line Items]                      
Net operating loss carryforwards 218,100,000               218,100,000    
Research and development tax credit carryforwards 15,900,000               15,900,000    
State and Local Jurisdiction | Minimum
                      
Income Tax Disclosure [Line Items]                      
Net operating loss carryforwards, expiration year                 2014    
State and Local Jurisdiction | Maximum
                      
Income Tax Disclosure [Line Items]                      
Net operating loss carryforwards, expiration year                 2033    
Cerus Europe B.V.
                      
Income Tax Disclosure [Line Items]                      
Undistributed earning of foreign subsidiary                 2,800,000    
Undistributed earnings, federal statutory income taxes                 $ 900,000