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Warrants - fair value of warrants (Details) - USD ($)	2 Months Ended	3 Months Ended		11 Months Ended	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Class of Warrant or Right [Line Items]
Changes in the fair value of warrants	$ 0	$ 2,646,000		$ 10,571,000
Evolv Technologies Holdings Inc [Member]
Class of Warrant or Right [Line Items]
Changes in the fair value of warrants		$ 736,000	$ 0
Evolv Technologies Holdings Inc [Member] | Maximum
Class of Warrant or Right [Line Items]
Changes in the fair value of warrants					$ 100,000	$ 100,000

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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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- Definition

Amount of expense (income) related to adjustment to fair value of warrant liability.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Section 25
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=109262497&loc=d3e20148-110875

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