Union Pension Plan - Summary of Multiple Employer Pension Plans (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Multiemployer Plans [Line Items]
Entity Tax Identification Number	83-2583782
Contributions of Alta Equipment Group Inc. and Subsidiaries	$ 2,468	$ 2,011
Operating Engineers I.U.O.E. Local 37 Pension Trust
Multiemployer Plans [Line Items]
Entity Tax Identification Number	52-6128064
Pension Protection Act Zone Status & Plan Year- End		Green
Pension Protection Act Zone Plan Year-End		Dec. 31, 2018
FIP/RP Status	No
Contributions of Alta Equipment Group Inc. and Subsidiaries		$ 10
Surcharge Imposed	No
Expiration Date of Collective-Bargaining	Mar. 31, 2020
Midwest Operating Engineers Local Union No. 150 Pension Trust Fund
Multiemployer Plans [Line Items]
Entity Tax Identification Number	36-6140097
Pension Protection Act Zone Status & Plan Year- End	Green	Green
Pension Protection Act Zone Plan Year-End	Mar. 31, 2020	Mar. 31, 2019
FIP/RP Status	No
Contributions of Alta Equipment Group Inc. and Subsidiaries	$ 1,472	$ 1,186
Surcharge Imposed	No
Expiration Date of Collective-Bargaining	May 31, 2021
Operating Engineers Local Union No. 324 Pension Fund
Multiemployer Plans [Line Items]
Entity Tax Identification Number	38-1900637
Pension Protection Act Zone Status & Plan Year- End	Red	Red
Pension Protection Act Zone Plan Year-End	Apr. 30, 2020	Apr. 30, 2019
FIP/RP Status	Implemented
Contributions of Alta Equipment Group Inc. and Subsidiaries	$ 783	$ 745
Surcharge Imposed	No
Expiration Date of Collective-Bargaining	Sep. 30, 2021
Central Pension Fund Of The International Union Of Operation Engineers Local Union No. 649 and 841
Multiemployer Plans [Line Items]
Entity Tax Identification Number	36-6052390
Pension Protection Act Zone Status & Plan Year- End	Green	Green
Pension Protection Act Zone Plan Year-End	Jan. 31, 2020	Jan. 31, 2019
FIP/RP Status	No
Contributions of Alta Equipment Group Inc. and Subsidiaries	$ 70	$ 70
Surcharge Imposed	No
Expiration Date of Collective-Bargaining	Mar. 31, 2021
Upstate New York Engineers Pension Fund Local Union 17C Engineers Local Union No. 639
Multiemployer Plans [Line Items]
Entity Tax Identification Number	15-0614642
Pension Protection Act Zone Status & Plan Year- End	Red
Pension Protection Act Zone Plan Year-End	Mar. 31, 2020
FIP/RP Status	Implemented
Contributions of Alta Equipment Group Inc. and Subsidiaries	$ 52
Surcharge Imposed	No
Expiration Date of Collective-Bargaining	Nov. 30, 2021
Central Pension Fund of Operating Engineers Local Union 17C
Multiemployer Plans [Line Items]
Entity Tax Identification Number	36-6052390
Pension Protection Act Zone Status & Plan Year- End	Green
Pension Protection Act Zone Plan Year-End	Jan. 31, 2020
FIP/RP Status	No
Contributions of Alta Equipment Group Inc. and Subsidiaries	$ 19
Surcharge Imposed	No
Expiration Date of Collective-Bargaining	Nov. 30, 2021
Central Pension Fund of the International Union of Operating Engineers Local 158 District 832
Multiemployer Plans [Line Items]
Entity Tax Identification Number	36-6052390
Pension Protection Act Zone Status & Plan Year- End	Green
Pension Protection Act Zone Plan Year-End	Jan. 31, 2020
FIP/RP Status	No
Contributions of Alta Equipment Group Inc. and Subsidiaries	$ 72
Surcharge Imposed	No
Expiration Date of Collective-Bargaining	Dec. 07, 2024
Central Pension Fund of International Union of Operating Engineers
Multiemployer Plans [Line Items]
Entity Tax Identification Number	36-6052390
Pension Protection Act Zone Status & Plan Year- End	Green
Pension Protection Act Zone Plan Year-End	Jan. 31, 2020
FIP/RP Status	No
Surcharge Imposed	No
Operating Engineers Local 825 Fund
Multiemployer Plans [Line Items]
Entity Tax Identification Number	22-6033380
Pension Protection Act Zone Status & Plan Year- End	Green
Pension Protection Act Zone Plan Year-End	Jun. 30, 2020
FIP/RP Status	No
Surcharge Imposed	No

The Tax Identification Number (TIN), also known as an Employer Identification Number (EIN), is a unique 9-digit value assigned by the IRS.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation 12B
-Number 240
-Section 12
-Subsection b-2

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Amount of cost for employer contribution to multiemployer plan. Multiemployer plan includes, but is not limited to, pension plan determined to be individually significant and insignificant and other postretirement benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 55
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Expiration date of collective-bargaining arrangement (CBA) requiring contribution to multiemployer pension plan determined to be individually insignificant, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 5
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947

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- Definition

Indicates whether funding improvement plan or rehabilitation plan was implemented or pending for multiemployer pension plan, determined to be individually insignificant. Acceptable values are "No", "Pending", "Implemented", "Other", and "NA".

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
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- Definition

Year-end date of plan applicable to certified zone status for multiemployer pension plan determined to be individually significant, in CCYY-MM-DD format.

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Indicates certified zone status of multiemployer pension plan determined to be individually significant. Acceptable values are "Green", "Yellow", "Orange", "Red", "Other", and "NA".

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Indicates whether employer paid surcharge to multiemployer pension plan determined to be individually significant. Acceptable values are "No", "Yes" and "NA".

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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