v3.8.0.1
Document And Entity Information - shares
3 Months Ended
Mar. 31, 2018
May 02, 2018
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 Mar. 31, 2018  
Document Fiscal Year Focus 2018  
Document Fiscal Period Focus Q1  
Amendment Flag false  
Common Class A [Member]    
Document Information [Line Items]    
Entity Common Stock, Shares Outstanding (in shares)   30,593,549
Common Class B [Member]    
Document Information [Line Items]    
Entity Common Stock, Shares Outstanding (in shares)   8,543,391