Note 11 - Share Based Compensation and Employee Benefit Plans (Details Textual) - USD ($)		12 Months Ended
	May 17, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 29, 2017	May 16, 2017	May 18, 2010	May 16, 2006
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross		472,463
Allocated Share-based Compensation Expense		$ 15,600,000	$ 12,900,000	$ 12,400,000
Proceeds from Stock Options Exercised		24,800,000	6,500,000	4,300,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value		25,000,000	4,800,000	2,600,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value		$ 6,300,000	$ 5,600,000	$ 5,100,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value		$ 12.33	$ 6.54	$ 11.27
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value		$ 31.37	$ 17.57	$ 24.75
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized		$ 13,400,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition		2 years 146 days
Deferred Compensation Plan [Member]
Deferred Compensation Arrangement with Individual, Vested Percentage		100.00%
Deferred Compensation Liability, Current		$ 9,800,000	$ 7,200,000
Cash Surrender Value of Life Insurance		$ 9,600,000	6,800,000
Rush 401 Plan [Member]
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay		10.00%
Defined Contribution Plan, Cost		$ 7,000,000	$ 6,500,000	$ 6,200,000
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%
Rush 401 Plan [Member] | Employees with More Than Five Years of Service [Member]
Defined Contribution Plan, Employer Matching Contribution, Percent of Match		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		$ 5,700,000
Common Class A [Member]
Share Price					$ 50.81
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 Additional Shares Authorized	500,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant		415,000
Common Stock, Capital Shares Reserved for Future Issuance		1,400,000
Stock Issued During Period, Shares, Employee Stock Purchase Plans		112,754	137,360
Number of Employees Eligible to Participate in Stock Purchase Plan		6,825
Number of Employees Participating in Stock Purchase Plan		1,131
The 2006 Non-Employee Director Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized								1,500,000
Reduction in Number of Shares Reserved for Issuance							1,000,000
Issuance of Cash for Non-employee Director Compensation, Percent		40.00%
Issuance of Stock and Cash for Non-employee Director Compensation		$ 125,000
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		152,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized		500,000
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures		13,393	27,038
The 2006 Non-Employee Director Stock Option Plan [Member] | Common Class A [Member] | Shares Issued to Two Nonemployee Directors [Member]
Share-based Goods and Nonemployee Services Transaction, Quantity of Securities Issued		3,307	6,145
The 2006 Non-Employee Director Stock Option Plan [Member] | Common Class A [Member] | Shares Issued to Four Non-employee Directors 2 [Member]
Issuance of Stock and Cash for Non-employee Director Compensation			$ 125,000
Share-based Goods and Nonemployee Services Transaction, Quantity of Securities Issued			3,687
Payment to Nonemployee Directors			$ 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		$ 125,000
Share-based Goods and Nonemployee Services Transaction, Quantity of Securities Issued		1,984
Payment to Nonemployee Directors		$ 50,000
The 2006 Non-Employee Director Stock Option Plan [Member] | Common Class A [Member] | Shares Issued to One Non-Employee Director 2 [Member]
Issuance of Stock and Cash for Non-employee Director Compensation		$ 125,000
Share-based Goods and Nonemployee Services Transaction, Quantity of Securities Issued		2,315
Payment to Nonemployee Directors		$ 37,500
The 2006 Non-Employee Director Stock Option Plan [Member] | Common Class A [Member] | Shares Issued to One Non-Employee Director 3 [Member]
Issuance of Stock and Cash for Non-employee Director Compensation		$ 125,000
Share-based Goods and Nonemployee Services Transaction, Quantity of Securities Issued		2,480
Payment to Nonemployee Directors		$ 31,250
Amended and Restated 2007 Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period		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		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		2,142,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized						7,800,000
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Number of Shares Per Employee		100,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross		472,463	493,088
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		1,063,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized						2,200,000
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Number of Shares Per Employee		100,000
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, Options, Grants in Period, Gross		274,390	268,890
Every 6 Months [Member] | Employee Stock Purchase Plan [Member]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount		$ 10,625