Document and Entity Information - shares	3 Months Ended
	Dec. 31, 2019	Jan. 22, 2020
Entity Information [Line Items]
Entity Current Reporting Status	Yes
Document Type	10-Q
Document Period End Date	Dec. 31, 2019
Amendment Flag	false
Document Fiscal Period Focus	Q1
Document Fiscal Year Focus	2020
Trading Symbol	FOR
Title of 12(b) Security	Common Stock, par value $1.00 per share
Entity Registrant Name	FORESTAR GROUP INC.
Entity Central Index Key	0001406587
Current Fiscal Year End Date	--09-30
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		48,025,359
Entity Shell Company	false
Entity Emerging Growth Company	false
Entity Small Business	false