Supplemental Guarantor Information (Condensed Consolidated Statements of Operations) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Aug. 31, 2017	Aug. 31, 2016	Aug. 31, 2017	Aug. 31, 2016
Condensed Consolidated Statements of Operations
Revenues		$ 1,144,001	$ 913,283	$ 2,965,391	$ 2,402,704
Homebuilding:
Revenues		1,140,787	910,111	2,957,105	2,394,315
Construction and land costs		(955,001)	(760,490)	(2,499,677)	(2,018,022)
Selling, general and administrative expenses		(109,095)	(98,144)	(305,901)	(279,886)
Operating income (loss)		76,691	51,477	151,527	96,407
Interest income		347	109	747	395
Interest expense	[1]	0	0	(6,307)	(5,667)
Intercompany Interest Income (Expense)		0	0	0	0
Equity in income (loss) of unconsolidated joint ventures				921	(2,616)
Total pretax income (loss)		79,208	53,463	152,649	94,287
Income tax expense	[2]	(29,000)	(14,100)	(56,400)	(26,200)
Income (Loss) from Subsidiaries, Net of Tax		0	0	0	0
Net income		50,208	39,363	96,249	68,087
KB Home Corporate
Condensed Consolidated Statements of Operations
Revenues		0	0	0	0
Homebuilding:
Revenues		0	0	0	0
Construction and land costs		0	0	0	0
Selling, general and administrative expenses		(23,220)	(23,436)	(68,809)	(66,752)
Operating income (loss)		(23,220)	(23,436)	(68,809)	(66,752)
Interest income		345	96	740	336
Interest expense		(41,746)	(46,485)	(131,788)	(135,192)
Intercompany Interest Income (Expense)		77,367	78,834	226,470	228,596
Total pretax income (loss)		12,746	9,009	26,613	26,988
Income tax expense		(3,700)	(1,600)	(4,900)	(3,700)
Income (Loss) from Subsidiaries, Net of Tax		41,162	31,954	74,536	44,799
Net income		50,208	39,363	96,249	68,087
Guarantor Subsidiaries
Condensed Consolidated Statements of Operations
Revenues		1,048,045	801,832	2,671,533	2,103,943
Homebuilding:
Revenues		1,048,045	801,832	2,671,533	2,103,943
Construction and land costs		(871,350)	(664,224)	(2,240,974)	(1,751,995)
Selling, general and administrative expenses		(72,686)	(64,541)	(206,513)	(182,015)
Operating income (loss)		104,009	73,067	224,046	169,933
Interest income		2	11	5	53
Interest expense		(434)	0	(1,428)	(1,641)
Intercompany Interest Income (Expense)		(31,059)	(27,997)	(87,524)	(82,984)
Total pretax income (loss)		71,704	44,545	134,421	83,400
Income tax expense		(26,200)	(12,300)	(52,300)	(24,600)
Income (Loss) from Subsidiaries, Net of Tax		0	0	0	0
Net income		45,504	32,245	82,121	58,800
Non-Guarantor Subsidiaries
Condensed Consolidated Statements of Operations
Revenues		95,956	111,451	293,858	298,761
Homebuilding:
Revenues		92,742	108,279	285,572	290,372
Construction and land costs		(83,651)	(96,266)	(258,703)	(266,027)
Selling, general and administrative expenses		(13,189)	(10,167)	(30,579)	(31,119)
Operating income (loss)		(4,098)	1,846	(3,710)	(6,774)
Interest income		0	2	2	6
Interest expense		(1,254)	0	(3,641)	(2,161)
Intercompany Interest Income (Expense)		(2,874)	(4,352)	(8,396)	(12,285)
Total pretax income (loss)		(5,242)	(91)	(8,385)	(16,101)
Income tax expense		900	(200)	800	2,100
Income (Loss) from Subsidiaries, Net of Tax		0	0	0	0
Net income		(4,342)	(291)	(7,585)	(14,001)
Homebuilding [Member]
Homebuilding:
Equity in income (loss) of unconsolidated joint ventures		(814)	(536)	(679)	(1,964)
Total pretax income (loss)		76,224	51,050	145,288	89,171
Homebuilding [Member] | KB Home Corporate
Homebuilding:
Equity in income (loss) of unconsolidated joint ventures		0	0	0	0
Total pretax income (loss)		12,746	9,009	26,613	26,988
Homebuilding [Member] | Guarantor Subsidiaries
Homebuilding:
Equity in income (loss) of unconsolidated joint ventures		(814)	(536)	(678)	(1,961)
Total pretax income (loss)		71,704	44,545	134,421	83,400
Homebuilding [Member] | Non-Guarantor Subsidiaries
Homebuilding:
Equity in income (loss) of unconsolidated joint ventures		0	0	(1)	(3)
Total pretax income (loss)		(8,226)	(2,504)	(15,746)	(21,217)
Financial services [Member]
Homebuilding:
Operating income (loss)		2,324	2,281	5,761	5,768
Equity in income (loss) of unconsolidated joint ventures		660	132	1,600	(652)
Total pretax income (loss)		2,984	2,413	7,361	5,116
Financial services [Member] | KB Home Corporate
Homebuilding:
Total pretax income (loss)		0	0	0	0
Financial services [Member] | Guarantor Subsidiaries
Homebuilding:
Total pretax income (loss)		0	0	0	0
Financial services [Member] | Non-Guarantor Subsidiaries
Homebuilding:
Total pretax income (loss)		2,984	2,413	7,361	5,116
Consolidating Adjustments
Condensed Consolidated Statements of Operations
Revenues		0	0	0	0
Homebuilding:
Revenues		0	0	0	0
Construction and land costs		0	0	0	0
Selling, general and administrative expenses		0	0	0	0
Operating income (loss)		0	0	0	0
Interest income		0	0	0	0
Interest expense		43,434	46,485	130,550	133,327
Intercompany Interest Income (Expense)		(43,434)	(46,485)	(130,550)	(133,327)
Total pretax income (loss)		0	0	0	0
Income tax expense		0	0	0	0
Income (Loss) from Subsidiaries, Net of Tax		(41,162)	(31,954)	(74,536)	(44,799)
Net income		(41,162)	(31,954)	(74,536)	(44,799)
Consolidating Adjustments | Homebuilding [Member]
Homebuilding:
Equity in income (loss) of unconsolidated joint ventures		0	0	0	0
Total pretax income (loss)		0	0	0	0
Consolidating Adjustments | Financial services [Member]
Homebuilding:
Total pretax income (loss)		$ 0	$ 0	$ 0	$ 0

[1] Interest incurred and interest expensed for the nine months ended August 31, 2017 included a charge of $5.7 million for the early extinguishment of debt

[2] (a) Amounts reflect the favorable net impact of federal energy tax credits we earned from building energy-efficient homes through December 31, 2016. The net impact of these tax credits was $2.6 million and $6.7 million for the three months ended August 31, 2017 and 2016, respectively, and $3.8 million and $10.4 million for the nine months ended August 31, 2017 and 2016, respectively.