Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Nov. 01, 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 Emerging Growth Company	false
Entity Small Business	false
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Amendment Flag	false
Common Class B [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding (in shares)		8,328,043
Common Class A [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding (in shares)		30,450,669