Document And Entity Information (USD $)
12 Months Ended
Jan. 03, 2012
Feb. 27, 2012
Jun. 28, 2011
Document And Entity Information [Abstract]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Jan. 03, 2012    
Document Fiscal Year Focus 2011    
Document Fiscal Period Focus FY    
Entity Registrant Name BJs RESTAURANTS INC    
Entity Central Index Key 0001013488    
Current Fiscal Year End Date --01-03    
Entity Filer Category Large Accelerated Filer    
Entity Common Stock, Shares Outstanding   27,912,557  
Entity Public Float     $ 1,243,024,427
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Well-known Seasoned Issuer No