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Stock-based Compensation - Additional Information (Detail) - Rocket Lab USA, Inc. - USD ($)
6 Months Ended 12 Months Ended
Jun. 30, 2021
Dec. 31, 2020
Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares authorized to issue under equity award plan 5,481,202 5,481,202  
Shares available for grant 626,110 858,632  
Options vesting period 4 years 4 years  
Options vesting on first anniversary of date of grant, percentage 25.00% 25.00%  
Unrecognized stock compensation expense $ 2,661,000 $ 4,303  
Options granted expected recognition period 4 years 4 years  
Performance-based Restricted Stock Units (RSUs) [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Options granted expected to be recognized period 4 years 4 years  
Unrecognized compensation expense $ 39,146 $ 15,749  
Shares granted to employees   657,239 761,430