v3.8.0.1
Document And Entity Information - shares
9 Months Ended
Sep. 30, 2017
Nov. 01, 2017
Document Information [Line Items]    
Entity Registrant Name RUSH ENTERPRISES INC \TX\  
Entity Central Index Key 0001012019  
Trading Symbol rusha  
Current Fiscal Year End Date --12-31  
Entity Filer Category Large Accelerated Filer  
Entity Current Reporting Status Yes  
Entity Voluntary Filers No  
Entity Well-known Seasoned Issuer Yes  
Document Type 10-Q  
Document Period End Date Sep. 30, 2017  
Document Fiscal Year Focus 2017  
Document Fiscal Period Focus Q3  
Amendment Flag false  
Common Class A [Member]    
Document Information [Line Items]    
Entity Common Stock, Shares Outstanding (in shares)   31,259,965
Common Class B [Member]    
Document Information [Line Items]    
Entity Common Stock, Shares Outstanding (in shares)   8,579,412