Evolv Technologies Holdings, Inc. General form of registration statement for all companies including face-amount certificate companies

Stock Based Compensation - Stock based compensation expenses (Details) - Evolv Technologies Holdings, Inc. - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	$ 535	$ 60	$ 1,617	$ 122	$ 662	$ 264
Cost of revenue
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	5	2	10	4	10	2
Sales and marketing
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	375	19	1,308	40	104	170
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	102	19	196	38	370	74
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	$ 53	$ 20	$ 103	$ 40	$ 178	$ 18