XML 12 R1.htm IDEA: XBRL DOCUMENT v3.25.3
Cover - shares
 9 Months Ended
Sep. 30, 2025
Nov. 14, 2025
Document Information [Line Items]    
Document Type 10-Q  
Document Quarterly Report true  
Document Transition Report false  
Entity Interactive Data Current Yes  
Amendment Flag false  
Document Period End Date Sep. 30, 2025  
Document Fiscal Year Focus 2025  
Document Fiscal Period Focus Q3  
Entity Information [Line Items]    
Entity Registrant Name TERRESTRIAL ENERGY INC.  
Entity Central Index Key 0002019804  
Entity File Number 001-42252  
Entity Tax Identification Number 98-1785406  
Entity Incorporation, State or Country Code DE  
Current Fiscal Year End Date --12-31  
Entity Current Reporting Status No  
Entity Shell Company true  
Entity Filer Category Non-accelerated Filer  
Entity Small Business true  
Entity Emerging Growth Company true  
Entity Ex Transition Period false  
Entity Contact Personnel [Line Items]    
Entity Address, Address Line One 2730 W. Tyvola Road  
Entity Address, Address Line Two Suite 100  
Entity Address, City or Town Charlotte  
Entity Address, State or Province NC  
Entity Address, Postal Zip Code 28217  
Entity Phone Fax Numbers [Line Items]    
City Area Code (646)  
Local Phone Number 687-8212  
Common Stock, par value $0.0001 per share    
Entity Listings [Line Items]    
Title of 12(b) Security Common Stock, par value $0.0001 per share  
Trading Symbol IMSR  
Security Exchange Name NASDAQ  
Redeemable Warrants, each whole warrant exercisable for one Common Stock at a price of $11.50 per share    
Entity Listings [Line Items]    
Title of 12(b) Security Redeemable Warrants, each whole warrant exercisable for one Common Stock at a price of $11.50 per share  
Trading Symbol IMSRW  
Security Exchange Name NASDAQ  
Class A Ordinary Shares    
Entity Listings [Line Items]    
Entity Common Stock, Shares Outstanding   22,992,610
Class B Ordinary Shares    
Entity Listings [Line Items]    
Entity Common Stock, Shares Outstanding   5,750,000