Summary of Quarterly Results of Operations (Unaudited) - Summary of Quarterly Results of Operations (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 64,497	$ 47,207	$ 47,992	$ 37,618	$ 105,392	$ 32,185	$ 43,625	$ 37,374	$ 197,314	$ 218,576	$ 238,164
Gross profit	17,352	17,403	(24,953)	18,579	46,655	12,879	21,060	18,012
Operating income (loss)	50,980	6,256	69,528	13,590	29,929	(8,482)	5,919	(3,424)	140,354	23,942	70,560
Equity in earnings of unconsolidated ventures	2,251	3,637	188	47	4,470	2,909	5,584	3,045	6,123	16,008	8,685
Income (loss) before taxes	51,069	7,163	26,591	5,992	26,747	(13,711)	3,382	(8,204)	92,346	8,890	57,547
Income (loss) discontinued operations, net of taxes	563	(7,164)	(2,048)	(8,216)	(39,482)	(106,937)	(36,992)	(2,719)	(16,865)	(186,130)	(19,609)
Net income (loss) attributable to Forestar Group Inc.	$ 43,745	$ 9,665	$ 9,614	$ (4,376)	$ (6,166)	$ (164,216)	$ (34,507)	$ (8,158)	$ 58,648	$ (213,047)	$ 16,583
Net income (loss) per share -- basic
Continuing operations, basic (usd per share)	$ 1.03	$ 0.40	$ 0.28	$ 0.11	$ 0.97	$ (1.67)	$ 0.07	$ (0.16)	$ 1.80	$ (0.79)	$ 0.84
Discontinued operations, basic (usd per share)	0.01	(0.17)	(0.05)	(0.24)	(1.15)	(3.12)	(1.08)	(0.08)	(0.40)	(5.43)	(0.46)
Net income (loss) per share - basic	1.04	0.23	0.23	(0.13)	(0.18)	(4.79)	(1.01)	(0.24)	1.40	(6.22)	0.38
Net income (loss) per share -- diluted
Continuing operations, diluted (usd per share)	1.02	0.40	0.28	0.09	0.79	(1.67)	0.06	(0.16)	1.78	(0.79)	0.83
Discontinued operations, diluted (usd per share)	0.01	(0.17)	(0.05)	(0.19)	(0.93)	(3.12)	(0.87)	(0.08)	(0.40)	(5.43)	(0.45)
Net income (loss) per share - diluted	$ 1.03	$ 0.23	$ 0.23	$ (0.10)	$ (0.14)	$ (4.79)	$ (0.81)	$ (0.24)	$ 1.38	$ (6.22)	$ 0.38
Continuing Operations
Supplemental Oil And Gas Reserve Information [Line Items]
Impairment of oil and gas properties	$ 3,874	$ 7,627	$ 48,826	$ 0	$ 315	$ 0	$ 225	$ 504
Discontinued Operations
Supplemental Oil And Gas Reserve Information [Line Items]
Impairment of oil and gas properties	$ 0	$ 0	$ 612	$ 0	$ 37,646	$ 81,240	$ 45,938	$ 7