Supplemental Guarantor Information (Condensed Consolidating Statements of Operations) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Nov. 30, 2019	Aug. 31, 2019	May 31, 2019	Feb. 28, 2019	Nov. 30, 2018	Aug. 31, 2018	May 31, 2018	Feb. 28, 2018	Nov. 30, 2019	Nov. 30, 2018	Nov. 30, 2017
Condensed Consolidated Statements of Operations
Total Revenues									$ 4,552,747	$ 4,547,002	$ 4,368,529
Home Building:
Total Revenues									4,552,747	4,547,002	4,368,529
Interest Expense									0	0	(622)
Equity in income (loss) of unconsolidated joint ventures									10,681	9,367	2,825
Gain (Loss) on Extinguishment of Debt									(6,800)	0	(5,685)
Pretax income (loss)	$ 164,967	$ 91,936	$ 56,761	$ 34,511	$ 128,936	$ 114,676	$ 78,308	$ 46,045	348,175	367,965	289,995
Income tax expense									(79,400)	(197,600)	(109,400)
Income (Loss) from Subsidiaries, Net of Tax									0	0	0
Net income	$ 123,167	$ 68,136	$ 47,461	$ 30,011	$ 96,836	$ 87,476	$ 57,308	$ (71,255)	268,775	170,365	180,595
Consolidating Adjustments
Condensed Consolidated Statements of Operations
Total Revenues									0	0	0
Home Building:
Total Revenues									0	0	0
Pretax income (loss)									0	0	0
Income tax expense									0	0	0
Income (Loss) from Subsidiaries, Net of Tax									(88,639)	(169,903)	(184,601)
Net income									(88,639)	(169,903)	(184,601)
Reportable Legal Entities [Member] | KB Home Corporate
Condensed Consolidated Statements of Operations
Total Revenues									0	0	0
Home Building:
Total Revenues									0	0	0
Pretax income (loss)									85,530	62,562	4,794
Income tax expense									(16,300)	(62,100)	(8,800)
Income (Loss) from Subsidiaries, Net of Tax									88,639	169,903	184,601
Net income									157,869	170,365	180,595
Reportable Legal Entities [Member] | Guarantor Subsidiaries
Condensed Consolidated Statements of Operations
Total Revenues									4,161,511	4,198,969	4,034,057
Home Building:
Total Revenues									4,161,511	4,198,969	4,034,057
Pretax income (loss)									248,280	308,667	271,770
Income tax expense									(58,100)	(101,200)	(100,000)
Income (Loss) from Subsidiaries, Net of Tax									0	0	0
Net income									190,180	207,467	171,770
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries
Condensed Consolidated Statements of Operations
Total Revenues									391,236	348,033	334,472
Home Building:
Total Revenues									391,236	348,033	334,472
Pretax income (loss)									14,365	(3,264)	13,431
Income tax expense									(5,000)	(34,300)	(600)
Income (Loss) from Subsidiaries, Net of Tax									0	0	0
Net income									9,365	(37,564)	12,831
Financial services
Condensed Consolidated Statements of Operations
Total Revenues									15,089	13,207	12,264
Home Building:
Total Revenues									15,089	13,207	12,264
Construction and land costs									(4,333)	(3,844)	(3,430)
Selling, general and administrative expenses									(4,333)	(3,844)	(3,430)
Operating Income (Loss)									10,756	9,363	8,834
Equity in income (loss) of unconsolidated joint ventures									12,230	7,301	4,234
Pretax income (loss)									22,986	16,664	13,068
Financial services | Consolidating Adjustments
Home Building:
Pretax income (loss)									0	0	0
Financial services | Reportable Legal Entities [Member] | KB Home Corporate
Home Building:
Pretax income (loss)									0	0	0
Financial services | Reportable Legal Entities [Member] | Guarantor Subsidiaries
Home Building:
Pretax income (loss)									0	0	0
Financial services | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries
Home Building:
Pretax income (loss)									22,986	16,664	13,068
Homebuilding:
Condensed Consolidated Statements of Operations
Total Revenues									4,537,658	4,533,795	4,356,265
Home Building:
Total Revenues									4,537,658	4,533,795	4,356,265
Construction and land costs									(3,708,928)	(3,743,920)	(3,646,468)
Selling, general and administrative expenses									(497,350)	(444,154)	(426,394)
Operating Income (Loss)									331,380	345,721	283,403
Interest income									2,158	3,514	1,240
Interest Expense									0	0	(622)
Intercompany Interest Income (Expense)									0	0	0
Equity in income (loss) of unconsolidated joint ventures									(1,549)	2,066	(1,409)
Gain (Loss) on Extinguishment of Debt									(6,800)		(5,685)
Pretax income (loss)									325,189	351,301	276,927
Homebuilding: | Consolidating Adjustments
Condensed Consolidated Statements of Operations
Total Revenues									0	0	0
Home Building:
Total Revenues									0	0	0
Construction and land costs									0	0	0
Selling, general and administrative expenses									0	0	0
Operating Income (Loss)									0	0	0
Interest income									0	0	0
Interest Expense									143,412	149,698	170,864
Intercompany Interest Income (Expense)									(143,412)	(149,698)	(170,864)
Equity in income (loss) of unconsolidated joint ventures									0	0	0
Gain (Loss) on Extinguishment of Debt									0		0
Pretax income (loss)									0	0	0
Homebuilding: | Reportable Legal Entities [Member] | KB Home Corporate
Condensed Consolidated Statements of Operations
Total Revenues									0	0	0
Home Building:
Total Revenues									0	0	0
Construction and land costs									0	0	0
Selling, general and administrative expenses									(100,630)	(101,152)	(91,120)
Operating Income (Loss)									(100,630)	(101,152)	(91,120)
Interest income									1,926	3,273	1,232
Interest Expense									(137,327)	(141,812)	(166,417)
Intercompany Interest Income (Expense)									328,361	302,253	266,784
Equity in income (loss) of unconsolidated joint ventures									0	0	0
Gain (Loss) on Extinguishment of Debt									(6,800)		(5,685)
Pretax income (loss)									85,530	62,562	4,794
Homebuilding: | Reportable Legal Entities [Member] | Guarantor Subsidiaries
Condensed Consolidated Statements of Operations
Total Revenues									4,161,511	4,198,969	4,034,057
Home Building:
Total Revenues									4,161,511	4,198,969	4,034,057
Construction and land costs									(3,362,386)	(3,435,058)	(3,342,617)
Selling, general and administrative expenses									(375,199)	(311,815)	(298,498)
Operating Income (Loss)									423,926	452,096	392,942
Interest income									23	11	8
Interest Expense									(746)	(2,624)	(1,635)
Intercompany Interest Income (Expense)									(173,374)	(142,882)	(118,138)
Equity in income (loss) of unconsolidated joint ventures									(1,549)	2,066	(1,407)
Gain (Loss) on Extinguishment of Debt									0		0
Pretax income (loss)									248,280	308,667	271,770
Homebuilding: | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries
Condensed Consolidated Statements of Operations
Total Revenues									376,147	334,826	322,208
Home Building:
Total Revenues									376,147	334,826	322,208
Construction and land costs									(346,542)	(308,862)	(303,851)
Selling, general and administrative expenses									(21,521)	(31,187)	(36,776)
Operating Income (Loss)									8,084	(5,223)	(18,419)
Interest income									209	230	0
Interest Expense									(5,339)	(5,262)	(3,434)
Intercompany Interest Income (Expense)									(11,575)	(9,673)	22,218
Equity in income (loss) of unconsolidated joint ventures									0	0	(2)
Gain (Loss) on Extinguishment of Debt									0		0
Pretax income (loss)									$ (8,621)	$ (19,928)	$ 363