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Maximum fair value for employee stock purchase per year.

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Payment to non-employee directors.

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Aggregate number of common shares reserved for future issuance.

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Unrecognized cost of unvested share-based compensation awards.

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The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Gross number of share options (or share units) granted during the period.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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The number of shares or units of entity securities issued in the transaction in which equity securities were issued to pay for goods or nonemployee services.

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Price of a single share of a number of saleable stocks of a company.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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Purchase price of common stock expressed as a percentage of its fair value.

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Note 11 - Share Based Compensation and Employee Benefit Plans (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	May 16, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	459,663
Allocated Share-based Compensation Expense, Total	$ 18,100,000	$ 15,600,000	$ 12,900,000
Proceeds from Stock Options Exercised	5,700,000	24,800,000	6,500,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value	2,700,000	25,000,000	4,800,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value	$ 5,700,000	$ 6,300,000	$ 5,600,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 15.46	$ 12.33	$ 6.54
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Total	$ 8,100,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	3 years 109 days
Deferred Compensation Plan [Member]
Deferred Compensation Arrangement with Individual, Vested Percentage	100.00%
Deferred Compensation Liability, Current, Total	$ 11,100,000	$ 9,800,000
Cash Surrender Value of Life Insurance	$ 8,900,000	9,600,000
Rush 401 Plan [Member]
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	10.00%
Defined Contribution Plan, Cost	$ 8,900,000	$ 7,000,000	$ 6,500,000
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	$ 6,600,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 40.46	$ 31.37	$ 17.57
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Total	$ 7,100,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	1 year 328 days
Common Class A [Member]
Share Price	$ 34.48
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	331,000
Common Stock, Capital Shares Reserved for Future Issuance	1,400,000
Stock Issued During Period, Shares, Employee Stock Purchase Plans	84,192	112,754
Number of Employees Eligible to Participate in Stock Purchase Plan	7,214
Number of Employees Participating in Stock Purchase Plan	1,495
The 2006 Non-Employee Director Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	500,000
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	140,300
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, Total	11,412	13,393
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	2,926	3,307
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	2,048	1,984
Payment to Nonemployee Directors	$ 37,500	$ 50,000
The 2006 Non-Employee Director Stock Option Plan [Member] \| Common Class A [Member] \| Shares Issued to Two Nonemployee 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	1,756
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]
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]
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	1,781,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	7,800,000			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	459,663	472,463
Amended and Restated 2007 Incentive Plan [Member] \| Common Class B [Member]
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, Number of Shares Available for Grant	762,000
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, Options, Grants in Period, Gross	306,590	274,390
Every 6 Months [Member] \| Employee Stock Purchase Plan [Member]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount	$ 10,625