Note 11 - Share Based Compensation and Employee Benefit Plans (Details Textual) - USD ($)				1 Months Ended	12 Months Ended
	Mar. 15, 2021	Jun. 16, 2020	Feb. 01, 2012	Oct. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	May 12, 2020
Share-based Payment Arrangement, Expense					$ 22,200,000	$ 19,400,000	$ 19,000,000.0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)					498,700
Proceeds from Stock Options Exercised					$ 18,300,000	23,500,000	11,100,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value					23,400,000	20,800,000	8,700,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value					$ 5,000,000.0	$ 4,500,000	$ 5,000,000.0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share)					$ 14.77	$ 6.36	$ 8.37
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total					$ 9,300,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)					2 years 2 months 12 days
Deferred Compensation Plan [Member]
Deferred Compensation Arrangement with Individual, Vested Percentage					100.00%
Deferred Compensation Liability, Current, Total					$ 21,300,000	$ 19,500,000
Cash Surrender Value of Life Insurance					12,700,000	11,500,000
Rush 401 Plan [Member]
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	10.00%	10.00%	10.00%
Defined Contribution Plan, Cost					$ 8,200,000	$ 6,000,000.0	$ 9,400,000
Rush 401 Plan [Member] | Highly Compensated Employees [Member]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent					15.00%
Rush 401 Plan [Member] | Employees with Less than Five Years of Service [Member]
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	20.00%	5.00%	20.00%
Rush 401 Plan [Member] | Employees with More Than Five Years of Service [Member]
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	40.00%	10.00%	40.00%
Rush 401 Plan [Member] | Minimum [Member]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent					1.00%
Rush 401 Plan [Member] | Maximum [Member]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent					50.00%
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value					$ 12,900,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share)					$ 44.86	$ 21.98	$ 26.91
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total					$ 9,200,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)					1 year 3 months 18 days
Common Class A [Member]
Share Price (in dollars per share)					$ 55.64
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent					85.00%
Maximum Fair Value for Employee Stock Purchase Per Year					$ 25,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares)					594,717
Common Stock, Capital Shares Reserved for Future Issuance (in shares)					2,700,000
Stock Issued During Period, Shares, Employee Stock Purchase Plans (in shares)					148,999	176,807
Number of Employees Eligible to Participate in Stock Purchase Plan					7,166
Number of Employees Participating in Stock Purchase Plan					1,854
The 2006 Non-Employee Director Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares)					750,000
Issuance of Stock and Cash for Non-employee Director Compensation					$ 145,000
Issuance of Cash for Non-employee Director Compensation, Percent					40.00%
The 2006 Non-Employee Director Stock Option Plan [Member] | Common Class A [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares)					148,152
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares)					750,000
Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture, Total (in shares)					15,726	25,128
The 2006 Non-Employee Director Stock Option Plan [Member] | Common Class A [Member] | Shares Issued to Three Non-employee Directors [Member]
Stock Issued During Period, Shares, New Issues (in shares)					2,875	5,235
The 2006 Non-Employee Director Stock Option Plan [Member] | Common Class A [Member] | Shares Issued to Two Nonemployee Directors [Member]
Issuance of Stock and Cash for Non-employee Director Compensation						$ 125,000
Stock Issued During Period, Shares, New Issues (in shares)					2,013	3,141
Payment to Nonemployee Directors					$ 43,500	$ 50,000
The 2006 Non-Employee Director Stock Option Plan [Member] | Common Class A [Member] | Shares Issued to One Nonemployee Director [Member]
Issuance of Stock and Cash for Non-employee Director Compensation					$ 145,000
Stock Issued During Period, Shares, New Issues (in shares)					1,725
Payment to Nonemployee Directors					$ 58,000
The 2006 Non-Employee Director Stock Option Plan [Member] | Common Class A [Member] | Shares Issued to One Director [Member]
Stock Issued During Period, Shares, New Issues (in shares)				1,350
Share-based Payment Arrangement, Expense				$ 72,500
Amended and Restated 2007 Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year)					10 years
Amended and Restated 2007 Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)					3 years
Amended and Restated 2007 Incentive Plan [Member] | Common Class A [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares)					2,243,779
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares)					13,200,000			13,200,000
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Number of Shares Per Employee (in shares)					150,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)					498,700	753,600
Amended and Restated 2007 Incentive Plan [Member] | Common Class B [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares)					1,308,825
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares)								4,800,000
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Number of Shares Per Employee (in shares)					150,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)					340,650	518,400
Amended and Restated 2007 Incentive Plan [Member] | Common Class B [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares)					4,800,000
Every 6 Months [Member] | Employee Stock Purchase Plan [Member]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount					$ 10,625