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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 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%
Total revenue | Credits Concentration Risk [Member] | Customer Representing More Than Ten Percentage        
Concentration Risk [Line Items]        
Concentration risk, percentage 28.30% 11.30%    
Total revenue | Credits Concentration Risk [Member] | Customer A        
Concentration Risk [Line Items]        
Concentration risk, percentage 18.30%      
Total revenue | Credits Concentration Risk [Member] | Customer B        
Concentration Risk [Line Items]        
Concentration risk, percentage 10.00%      
Total revenue | Credits Concentration Risk [Member] | Customer H        
Concentration Risk [Line Items]        
Concentration risk, percentage   11.30%    
Accounts receivable | Customer concentration risk        
Concentration Risk [Line Items]        
Number of customers 0   2  
Accounts receivable | Credits Concentration Risk [Member] | Customer Representing More Than Ten Percentage        
Concentration Risk [Line Items]        
Concentration risk, percentage     47.20%  
Accounts receivable | Credits Concentration Risk [Member] | Customer F        
Concentration Risk [Line Items]        
Concentration risk, percentage 23.80%   23.40%