v3.26.1
Cover - shares
 3 Months Ended
Mar. 31, 2026
Apr. 28, 2026
Document Information [Line Items]    
Document Type 10-Q  
Document Quarterly Report true  
Document Transition Report false  
Amendment Flag false  
Document Period End Date Mar. 31, 2026  
Document Fiscal Year Focus 2026  
Document Fiscal Period Focus Q1  
Entity Registrant Name BEST SPAC I ACQUISITION CORP.  
Entity Central Index Key 0002051587  
Entity Incorporation, State or Country Code D8  
Current Fiscal Year End Date --12-31  
Entity Filer Category Non-accelerated Filer  
Entity Small Business true  
Entity Emerging Growth Company true  
Entity Ex Transition Period false  
City Area Code +852  
Local Phone Number 9828 3397  
Entity Shell Company true  
Entity Interactive Data Current Yes  
Entity Current Reporting Status Yes  
Entity File Number 001-42700  
Entity Address, Address Line One 701, 7/FloorUnited Building  
Entity Address, Address Line Two 17-19 Jubilee Street  
Entity Address, City or Town Hong Kong  
Entity Address, Country HK  
Entity Address, Postal Zip Code 00000  
Entity Tax Identification Number 00-0000000  
Class A Ordinary Shares    
Document Information [Line Items]    
Entity Common Stock, Shares Outstanding   6,024,500
Class B Ordinary Shares    
Document Information [Line Items]    
Entity Common Stock, Shares Outstanding   1,375,000
Units    
Document Information [Line Items]    
Title of 12(b) Security Units  
Trading Symbol BSAAU  
Security Exchange Name NASDAQ  
Class A ordinary shares, no par value    
Document Information [Line Items]    
Title of 12(b) Security Class A ordinary shares, no par value  
Trading Symbol BSAA  
Security Exchange Name NASDAQ  
Rights    
Document Information [Line Items]    
Title of 12(b) Security Rights  
Trading Symbol BSAAR  
Security Exchange Name NASDAQ