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Summary of Significant Accounting Policies - Risk of concentrations of credit, significant customers and significant suppliers (Details)

v3.21.2
Summary of Significant Accounting Policies - Risk of concentrations of credit, significant customers and significant suppliers (Details) - Evolv Technologies Holdings, Inc. - customer
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Total revenue | Customer concentration risk | Customer Representing More Than Ten Percentage    
Concentration Risk [Line Items]    
Concentration risk, percentage 10.70% 59.50%
Total revenue | Customer concentration risk | Customer One    
Concentration Risk [Line Items]    
Number of customers 1  
Concentration risk, percentage 10.00%  
Total revenue | Customer concentration risk | Customer Three    
Concentration Risk [Line Items]    
Number of customers   3
Concentration risk, percentage   10.00%
Total revenue | Customer concentration risk | Customer A    
Concentration Risk [Line Items]    
Concentration risk, percentage 10.70%  
Total revenue | Customer concentration risk | Customer B    
Concentration Risk [Line Items]    
Concentration risk, percentage   26.60%
Total revenue | Customer concentration risk | Customer C    
Concentration Risk [Line Items]    
Concentration risk, percentage   21.70%
Total revenue | Customer concentration risk | Customer D    
Concentration Risk [Line Items]    
Concentration risk, percentage   11.20%
Accounts receivable | Customer concentration risk | Customer Two    
Concentration Risk [Line Items]    
Number of customers 2 2
Concentration risk, percentage 10.00% 10.00%
Accounts receivable | Credit concentration risk | Customer Representing More Than Ten Percentage    
Concentration Risk [Line Items]    
Concentration risk, percentage 47.20% 78.20%
Accounts receivable | Credit concentration risk | Customer C    
Concentration Risk [Line Items]    
Concentration risk, percentage   56.30%
Accounts receivable | Credit concentration risk | Customer E    
Concentration Risk [Line Items]    
Concentration risk, percentage 23.80%  
Accounts receivable | Credit concentration risk | Customer F    
Concentration Risk [Line Items]    
Concentration risk, percentage 23.40%  
Accounts receivable | Credit concentration risk | Customer G    
Concentration Risk [Line Items]    
Concentration risk, percentage   21.90%