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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 [Member] - customer
3 Months Ended 12 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Dec. 31, 2020
Dec. 31, 2019
Total revenue | Customer concentration risk        
Concentration Risk [Line Items]        
Number of customers 2 1    
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        
Concentration Risk [Line Items]        
Number of customers 0   2  
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%