Supplemental Guarantor Information (Condensed Consolidated Statements of Operations) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Aug. 31, 2018	Aug. 31, 2017	Aug. 31, 2018	Aug. 31, 2017
Condensed Consolidated Statements of Operations
Revenues		$ 1,225,347	$ 1,144,001	$ 3,198,393	$ 2,965,391
Homebuilding:
Revenues		1,221,875	1,140,787	3,189,753	2,957,105
Construction and land costs		(1,001,509)	(955,001)	(2,642,231)	(2,499,677)
Selling, general and administrative expenses		(114,753)	(109,095)	(323,708)	(305,901)
Operating income (loss)		105,613	76,691	223,814	151,527
Interest income		458	347	2,739	747
Interest expense	[1]	0	0	0	(6,307)
Intercompany Interest Income (Expense)		0	0	0	0
Equity in income of unconsolidated joint ventures				6,691	921
Total pretax income (loss)		114,676	79,208	239,029	152,649
Income tax expense		(27,200)	(29,000)	(165,500)	(56,400)
Income (Loss) from Subsidiaries, Net of Tax		0	0	0	0
Net income		87,476	50,208	73,529	96,249
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		(24,688)	(23,220)	(73,669)	(68,809)
Operating income (loss)		(24,688)	(23,220)	(73,669)	(68,809)
Interest income		380	345	2,559	740
Interest expense		(33,319)	(41,746)	(109,233)	(131,788)
Intercompany Interest Income (Expense)		78,519	77,367	226,642	226,470
Total pretax income (loss)		20,892	12,746	46,299	26,613
Income tax expense		(3,500)	(3,700)	(50,600)	(4,900)
Income (Loss) from Subsidiaries, Net of Tax		70,084	41,162	77,830	74,536
Net income		87,476	50,208	73,529	96,249
Guarantor Subsidiaries
Condensed Consolidated Statements of Operations
Revenues		1,115,373	1,048,045	2,886,995	2,671,533
Homebuilding:
Revenues		1,115,373	1,048,045	2,886,995	2,671,533
Construction and land costs		(907,027)	(871,350)	(2,376,223)	(2,240,974)
Selling, general and administrative expenses		(80,196)	(72,686)	(223,023)	(206,513)
Operating income (loss)		128,150	104,009	287,749	224,046
Interest income		0	2	9	5
Interest expense		(669)	(434)	(1,992)	(1,428)
Intercompany Interest Income (Expense)		(39,896)	(31,059)	(103,211)	(87,524)
Total pretax income (loss)		91,078	71,704	184,882	134,421
Income tax expense		(22,700)	(26,200)	(88,500)	(52,300)
Income (Loss) from Subsidiaries, Net of Tax		0	0	0	0
Net income		68,378	45,504	96,382	82,121
Non-Guarantor Subsidiaries
Condensed Consolidated Statements of Operations
Revenues		109,974	95,956	311,398	293,858
Homebuilding:
Revenues		106,502	92,742	302,758	285,572
Construction and land costs		(94,482)	(83,651)	(266,008)	(258,703)
Selling, general and administrative expenses		(9,869)	(13,189)	(27,016)	(30,579)
Operating income (loss)		2,151	(4,098)	9,734	(3,710)
Interest income		78	0	171	2
Interest expense		(1,240)	(1,254)	(3,871)	(3,641)
Intercompany Interest Income (Expense)		(3,395)	(2,874)	(8,335)	(8,396)
Total pretax income (loss)		2,706	(5,242)	7,848	(8,385)
Income tax expense		(1,000)	900	(26,400)	800
Income (Loss) from Subsidiaries, Net of Tax		0	0	0	0
Net income		1,706	(4,342)	(18,552)	(7,585)
Homebuilding [Member]
Homebuilding:
Equity in income of unconsolidated joint ventures		3,493	(814)	2,326	(679)
Total pretax income (loss)		109,564	76,224	228,879	145,288
Homebuilding [Member] | KB Home Corporate
Homebuilding:
Equity in income of unconsolidated joint ventures		0	0	0	0
Total pretax income (loss)		20,892	12,746	46,299	26,613
Homebuilding [Member] | Guarantor Subsidiaries
Homebuilding:
Equity in income of unconsolidated joint ventures		3,493	(814)	2,327	(678)
Total pretax income (loss)		91,078	71,704	184,882	134,421
Homebuilding [Member] | Non-Guarantor Subsidiaries
Homebuilding:
Equity in income of unconsolidated joint ventures		0	0	(1)	(1)
Total pretax income (loss)		(2,406)	(8,226)	(2,302)	(15,746)
Financial services [Member]
Homebuilding:
Operating income (loss)		2,527	2,324	5,785	5,761
Equity in income of unconsolidated joint ventures		2,585	660	4,365	1,600
Total pretax income (loss)		5,112	2,984	10,150	7,361
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)		5,112	2,984	10,150	7,361
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		35,228	43,434	115,096	130,550
Intercompany Interest Income (Expense)		(35,228)	(43,434)	(115,096)	(130,550)
Total pretax income (loss)		0	0	0	0
Income tax expense		0	0	0	0
Income (Loss) from Subsidiaries, Net of Tax		(70,084)	(41,162)	(77,830)	(74,536)
Net income		(70,084)	(41,162)	(77,830)	(74,536)
Consolidating Adjustments | Homebuilding [Member]
Homebuilding:
Equity in income 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