v3.8.0.1
Document And Entity Information - USD ($)
12 Months Ended
Dec. 31, 2017
Feb. 16, 2018
Jun. 30, 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    
Entity Public Float     $ 1,310,859,219
Document Type 10-K    
Document Period End Date Dec. 31, 2017    
Document Fiscal Year Focus 2017    
Document Fiscal Period Focus FY    
Amendment Flag false    
Common Class A [Member]      
Document Information [Line Items]      
Entity Common Stock, Shares Outstanding (in shares)   31,400,734  
Common Class B [Member]      
Document Information [Line Items]      
Entity Common Stock, Shares Outstanding (in shares)   8,433,777