Summary of Quarterly Results of Operations - Summary of Quarterly Results of Operations (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended																12 Months Ended
		Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015		Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Impairment of Oil and Gas Properties		$ 37,646		$ 81,240		$ 45,938		$ 7		$ 30,591		$ 735		$ 584		$ 755		$ 164,831	$ 32,665
Total revenues		114,018	[1]	43,168	[1]	57,430	[1]	47,805	[1]	80,316	[1]	58,840	[1]	83,013	[1]	84,605	[1]	262,421	306,774	$ 331,045
Gross profit	[1]	8,341		(69,572)		(35,009)		17,289		(6,259)		19,606		33,261		35,025
Operating income (loss)		(9,482)	[1]	(94,751)	[1]	(52,714)	[1]	(7,737)	[1]	(16,783)	[1]	12,716	[1]	26,942	[1]	15,883	[1]	(164,684)	38,758	46,577
Equity in earnings of unconsolidated ventures		4,470	[1]	2,909	[1]	5,584	[1]	3,045	[1]	4,720	[1]	2,016	[1]	958	[1]	991	[1]	16,008	8,685	8,737
Income (loss) before taxes		(11,983)	[1]	(100,095)	[1]	(55,062)	[1]	(12,596)	[1]	(18,713)	[1]	7,994	[1]	22,799	[1]	13,665	[1]	(179,736)	25,745	42,269
Net income (loss) attributable to Forestar Group Inc.		$ (6,166)	[1]	$ (164,216)	[1]	$ (34,507)	[1]	$ (8,158)	[1]	$ (11,800)	[1]	$ 5,227	[1]	$ 14,822	[1]	$ 8,334	[1]	$ (213,047)	$ 16,583	$ 29,321
Net income (loss) per share - basic		$ (0.18)	[1]	$ (4.79)	[1]	$ (1.01)	[1]	$ (0.24)	[1]	$ (0.34)	[1]	$ 0.12	[1]	$ 0.34	[1]	$ 0.20	[1]	$ (6.22)	$ 0.38	$ 0.81
Net income (loss) per share - diluted		$ (0.18)	[1]	$ (4.79)	[1]	$ (1.01)	[1]	$ (0.24)	[1]	$ (0.34)	[1]	$ 0.12	[1]	$ 0.34	[1]	$ 0.19	[1]	$ (6.22)	$ 0.38	$ 0.80

[1] Non-cash impairment charges for unproved leasehold interests and proved oil and gas properties included in our quarterly financial results are as follows: First Quarter Second Quarter Third Quarter FourthQuarter (In thousands)2015$7 $45,938 $81,240 $37,6462014755 584 735 30,591