Note 2 - Other Assets (Details Textual) $ in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Apr. 25, 2019 CAD ($)	Feb. 25, 2019	Dec. 31, 2018 USD ($)
Capitalized Computer Software, Net, Ending Balance	$ 9,400		$ 9,400
Capitalized Computer Software, Amortization	500	$ 500	1,400	$ 21,200
Indefinite-Lived Franchise Rights	7,000		7,000				$ 7,000
Goodwill and Intangible Asset Impairment, Total			0
Financial Guarantee [Member]
Guarantor Obligations, Maximum Exposure, Undiscounted					$ 250
Other Noncurrent Liabilities [Member] | Financial Guarantee [Member]
Guarantor Obligations, Current Carrying Value	5,000		5,000
Rush Truck Centres of Canada Limited [Member]
Equity Method Investment, Ownership Percentage						50.00%
Rush Truck Centres of Canada Limited [Member] | Other Assets [Member]
Equity Method Investments	25,200		25,200
Rush Truck Centres of Canada Limited [Member] | Call Option [Member]
Equity Method Investment, Remaining Ownership Percentage Not Yet Acquired						50.00%
Rush Truck Centres of Canada Limited [Member] | Call Option [Member] | Other Assets [Member]
Call Option, Fair Value Disclosure	3,600		3,600
Computer Software, Intangible Asset [Member]
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	1,900		1,900
Finite-Lived Intangible Assets, Amortization Expense, Year Two	1,900		1,900
Finite-Lived Intangible Assets, Amortization Expense, Year Three	1,900		1,900
Finite-Lived Intangible Assets, Amortization Expense, Year Four	1,900		1,900
Finite-Lived Intangible Assets, Amortization Expense, Year Five	$ 1,900		$ 1,900
Components of ERP Platform Rquired Replacement [Member]
Capitalized Computer Software, Amortization				$ 19,900