Business Combinations - Summary of Pro Forma Statement of Operations (Details) - USD ($) $ in Millions	11 Months Ended	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Revenues:
Net revenue		$ 873.6	$ 557.4
Cost of revenues:
Cost of revenue		659.1	405.3
Gross profit		214.5	152.1
General and administrative expenses			137.6
Depreciation and amortization expense		6.6	2.8
Total general and administrative expenses		222.6	140.4
(Loss) income from operations		(8.1)	11.7
Other income (expense)
Interest expense		(23.8)	(20.5)
Other income		8.9	1.3
Change in fair market value of warrants			(27.9)
Total other income (expense)		(22.5)	(47.1)
Loss before taxes	$ (20.7)	(30.6)	(35.4)
Income tax benefit		(6.6)	0.0
Net loss		(24.0)	(35.4)
Pro Forma
Cost of revenues:
General and administrative expenses			(0.3)
Total general and administrative expenses			(0.3)
(Loss) income from operations			0.3
Other income (expense)
Interest expense			(1.0)
Total other income (expense)			(1.0)
Loss before taxes			(0.7)
Net loss			(0.7)
Alta Equipment Holdings, Inc. | Pro Forma
Revenues:
Net revenue			557.4
Cost of revenues:
Cost of revenue			405.3
Gross profit			152.1
General and administrative expenses			137.3
Depreciation and amortization expense			2.8
Total general and administrative expenses			140.1
(Loss) income from operations			12.0
Other income (expense)
Interest expense			(21.5)
Other income			1.3
Change in fair market value of warrants			(27.9)
Total other income (expense)			(48.1)
Loss before taxes			(36.1)
Net loss			(36.1)
Northland Industrial Truck Co., Inc | Pro Forma
Revenues:
Net revenue			45.2
Cost of revenues:
Cost of revenue			31.5
Gross profit			13.7
General and administrative expenses			12.5
Depreciation and amortization expense			0.2
Total general and administrative expenses			12.7
(Loss) income from operations			1.0
Other income (expense)
Interest expense			(0.2)
Other income			0.4
Total other income (expense)			0.2
Loss before taxes			1.2
Net loss			1.2
FlaglerCE Holdings LLC
Revenues:
Net revenue		25.8
Other income (expense)
Net loss		(0.1)
FlaglerCE Holdings LLC | Pro Forma
Revenues:
Net revenue			177.0
Cost of revenues:
Cost of revenue			148.1
Gross profit			28.9
General and administrative expenses			27.2
Depreciation and amortization expense			1.0
Total general and administrative expenses			28.2
(Loss) income from operations			0.7
Other income (expense)
Interest expense			(0.9)
Other income			0.5
Total other income (expense)			(0.4)
Loss before taxes			0.3
Net loss			0.3
Consolidate Entities And Flagler C E Holdings L L C And Northern Industrial Truck Corporation | Pro Forma
Revenues:
Net revenue			779.6
Cost of revenues:
Cost of revenue			584.9
Gross profit			194.7
General and administrative expenses			177.0
Depreciation and amortization expense			4.0
Total general and administrative expenses			181.0
(Loss) income from operations			13.7
Other income (expense)
Interest expense			(22.6)
Other income			2.2
Change in fair market value of warrants			(27.9)
Total other income (expense)			(48.3)
Loss before taxes			(34.6)
Net loss			(34.6)
New, Used and Rental Equipment Sales
Revenues:
Net revenue			286.8
Cost of revenues:
Cost of revenue			251.8
New, Used and Rental Equipment Sales | Alta Equipment Holdings, Inc. | Pro Forma
Revenues:
Net revenue			286.8
Cost of revenues:
Cost of revenue			251.8
New, Used and Rental Equipment Sales | Northland Industrial Truck Co., Inc | Pro Forma
Revenues:
Net revenue			24.5
Cost of revenues:
Cost of revenue			21.7
New, Used and Rental Equipment Sales | FlaglerCE Holdings LLC | Pro Forma
Revenues:
Net revenue			114.2
Cost of revenues:
Cost of revenue			102.0
New, Used and Rental Equipment Sales | Consolidate Entities And Flagler C E Holdings L L C And Northern Industrial Truck Corporation | Pro Forma
Revenues:
Net revenue			425.5
Cost of revenues:
Cost of revenue			375.5
Parts Sales
Revenues:
Net revenue		129.6	82.7
Cost of revenues:
Cost of revenue		89.1	54.1
Parts Sales | Alta Equipment Holdings, Inc. | Pro Forma
Revenues:
Net revenue			82.7
Cost of revenues:
Cost of revenue			54.1
Parts Sales | Northland Industrial Truck Co., Inc | Pro Forma
Revenues:
Net revenue			6.5
Cost of revenues:
Cost of revenue			3.7
Parts Sales | FlaglerCE Holdings LLC | Pro Forma
Revenues:
Net revenue			30.2
Cost of revenues:
Cost of revenue			23.5
Parts Sales | Consolidate Entities And Flagler C E Holdings L L C And Northern Industrial Truck Corporation | Pro Forma
Revenues:
Net revenue			119.4
Cost of revenues:
Cost of revenue			81.3
Service Revenue
Revenues:
Net revenue		128.5	92.7
Cost of revenues:
Cost of revenue		49.5	34.6
Service Revenue | Alta Equipment Holdings, Inc. | Pro Forma
Revenues:
Net revenue			92.7
Cost of revenues:
Cost of revenue			34.6
Service Revenue | Northland Industrial Truck Co., Inc | Pro Forma
Revenues:
Net revenue			8.3
Cost of revenues:
Cost of revenue			2.0
Service Revenue | FlaglerCE Holdings LLC | Pro Forma
Revenues:
Net revenue			15.3
Cost of revenues:
Cost of revenue			8.5
Service Revenue | Consolidate Entities And Flagler C E Holdings L L C And Northern Industrial Truck Corporation | Pro Forma
Revenues:
Net revenue			116.3
Cost of revenues:
Cost of revenue			45.1
Rental Revenue
Revenues:
Net revenue		118.8	95.2
Cost of revenues:
Cost of revenue		20.2	17.5
Rental Revenue | Alta Equipment Holdings, Inc. | Pro Forma
Revenues:
Net revenue			95.2
Cost of revenues:
Cost of revenue			17.5
Rental Revenue | Northland Industrial Truck Co., Inc | Pro Forma
Revenues:
Net revenue			5.9
Cost of revenues:
Cost of revenue			0.6
Rental Revenue | FlaglerCE Holdings LLC | Pro Forma
Revenues:
Net revenue			17.3
Cost of revenues:
Cost of revenue			2.1
Rental Revenue | Consolidate Entities And Flagler C E Holdings L L C And Northern Industrial Truck Corporation | Pro Forma
Revenues:
Net revenue			118.4
Cost of revenues:
Cost of revenue			20.2
Rental Depreciation
Cost of revenues:
Cost of revenue		$ 68.4	47.3
Rental Depreciation | Alta Equipment Holdings, Inc. | Pro Forma
Cost of revenues:
Cost of revenue			47.3
Rental Depreciation | Northland Industrial Truck Co., Inc | Pro Forma
Cost of revenues:
Cost of revenue			3.5
Rental Depreciation | FlaglerCE Holdings LLC | Pro Forma
Cost of revenues:
Cost of revenue			12.0
Rental Depreciation | Consolidate Entities And Flagler C E Holdings L L C And Northern Industrial Truck Corporation | Pro Forma
Cost of revenues:
Cost of revenue			$ 62.8