v3.25.2
Document and Entity Information - shares
 9 Months Ended
Jun. 30, 2025
Jul. 18, 2025
Entity Information [Line Items]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Jun. 30, 2025  
Document Transition Report false  
Entity File Number 001-33662  
Entity Registrant Name FORESTAR GROUP INC.  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 26-1336998  
Entity Address, Address Line One 2221 E. Lamar Blvd.  
Entity Address, Address Line Two Suite 790  
Entity Address, City or Town Arlington  
Entity Address, State or Province TX  
Entity Address, Postal Zip Code 76006  
City Area Code 817  
Local Phone Number 769-1860  
Title of 12(b) Security Common Stock, par value $1.00 per share  
Trading Symbol FOR  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Large Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   50,833,171
Current Fiscal Year End Date --09-30  
Amendment Flag false  
Document Fiscal Year Focus 2025  
Document Fiscal Period Focus Q3  
Entity Central Index Key 0001406587  
NYSE CHICAGO, INC.    
Entity Information [Line Items]    
Security Exchange Name CHX  
NEW YORK STOCK EXCHANGE, INC.    
Entity Information [Line Items]    
Security Exchange Name NYSE