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Payment to non-employee directors.

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Carrying amount as of the balance sheet date of amounts which could be received based on the terms of the insurance contract upon surrendering life policies owned by the entity.

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Aggregate number of common shares reserved for future issuance.

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Aggregate carrying value as of the balance sheet date of the liabilities for all deferred compensation arrangements payable within one year (or the operating cycle, if longer). Represents currently earned compensation under compensation arrangements that is not actually paid until a later date.

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Amount of cost for defined contribution plan.

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Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Amount of cash inflow from exercise of option under share-based payment arrangement.

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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The highest quantity of shares an employee can purchase under the plan per period.

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Number of shares authorized for issuance under share-based payment arrangement.

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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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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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Note 11 - Share Based Compensation and Employee Benefit Plans (Details Textual) - USD ($)		12 Months Ended
	Jun. 16, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	May 12, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)		753,600
Share-based Payment Arrangement, Expense		$ 19,400,000	$ 19,000,000.0	$ 18,100,000
Proceeds from Stock Options Exercised		23,500,000	11,100,000	5,700,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value		20,800,000	8,700,000	2,700,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value		$ 4,500,000	$ 5,000,000.0	$ 5,700,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share)		$ 6.36	$ 8.37	$ 10.31
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total		$ 8,000,000.0
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)		2 years 1 month 6 days
Deferred Compensation Plan [Member]
Deferred Compensation Arrangement with Individual, Vested Percentage		100.00%
Deferred Compensation Liability, Current, Total		$ 19,500,000	$ 15,600,000
Cash Surrender Value of Life Insurance		$ 11,500,000	10,600,000
Rush 401 Plan [Member]
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	10.00%	10.00%
Defined Contribution Plan, Cost		$ 6,000,000.0	$ 9,400,000	$ 8,900,000
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	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	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		$ 11,800,000
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)		$ 21.98	$ 26.91	$ 26.97
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total		$ 7,800,000
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)		$ 41.42
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 Authorized (in shares)					600,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares)		743,716
Common Stock, Capital Shares Reserved for Future Issuance (in shares)		2,700,000
Stock Issued During Period, Shares, Employee Stock Purchase Plans (in shares)		176,807	175,925
Number of Employees Eligible to Participate in Stock Purchase Plan		6,307
Number of Employees Participating in Stock Purchase Plan		1,650
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 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 Authorized (in shares)		750,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares)		163,878
Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture, Total (in shares)		25,128	21,560
The 2006 Non-Employee Director Stock Option Plan [Member] \| Common Class A [Member] \| Shares Issued to Three Non-employee Directors [Member]
Share-based Goods and Nonemployee Services Transaction, Quantity of Securities Issued (in shares)		5,235	4,756
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		$ 125,000
Share-based Goods and Nonemployee Services Transaction, Quantity of Securities Issued (in shares)		3,141	2,854
Payment to Nonemployee Directors		$ 50,000	$ 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			$ 62,500
Share-based Goods and Nonemployee Services Transaction, Quantity of Securities Issued (in shares)			1,584
Payment to Nonemployee Directors			$ 18,750
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 Authorized (in shares)		13,200,000			13,200,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares)		2,736,479
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)		753,600	723,995
Amended and Restated 2007 Incentive Plan [Member] \| Common Class B [Member]
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, Number of Shares Available for Grant (in shares)		1,648,275
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)		518,400	476,385
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