Supplemental Guarantor Information (Condensed Consolidated Balance Sheets) (Details) - USD ($) $ in Thousands		Aug. 31, 2020	May 31, 2020	Nov. 30, 2019	Aug. 31, 2019	May 31, 2019	Nov. 30, 2018
Assets
Cash and cash equivalents		$ 723,126		$ 454,858	$ 184,837		$ 575,119
Receivables		269,651		249,055
Inventories		3,671,129		3,704,602
Property and equipment, net		64,619		65,043
Other assets		125,242		83,041
Total assets		5,177,427		5,015,482
Liabilities and stockholders’ equity
Mortgages and notes payable		1,747,704		1,748,747
Intercompany payables		0		0
Stockholders’ equity		2,565,308	$ 2,490,354	2,383,122	2,262,229	$ 2,195,210	2,087,500
Total liabilities and stockholders’ equity		5,177,427		5,015,482
Reportable Legal Entities [Member] | KB Home Corporate [Member]
Assets
Cash and cash equivalents		649,859		357,966	67,247		429,977
Total assets		4,513,881		4,298,971
Liabilities and stockholders’ equity
Intercompany payables		87,687		60,964
Stockholders’ equity		2,565,308		2,383,122
Total liabilities and stockholders’ equity		4,513,881		4,298,971
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents		43,395		65,434	104,043		114,269
Total assets		3,813,832		3,981,908
Liabilities and stockholders’ equity
Intercompany payables		3,312,907		3,520,090
Stockholders’ equity		61,241		0
Total liabilities and stockholders’ equity		3,813,832		3,981,908
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents		29,872		31,458	13,547		30,873
Total assets		679,851		660,459
Liabilities and stockholders’ equity
Intercompany payables		299,674		229,049
Stockholders’ equity		68,628		115,753
Total liabilities and stockholders’ equity		679,851		660,459
Consolidating Adjustments [Member]
Assets
Cash and cash equivalents		0		0	0		$ 0
Total assets		(3,830,137)		(3,925,856)
Liabilities and stockholders’ equity
Intercompany payables		(3,700,268)		(3,810,103)
Stockholders’ equity		(129,869)		(115,753)
Total liabilities and stockholders’ equity		(3,830,137)		(3,925,856)
Home Building [Member]
Assets
Cash and cash equivalents		722,033		453,814	183,794
Receivables		269,651		249,055
Inventories		3,671,129		3,704,602
Investments in unconsolidated joint ventures		48,821		57,038
Property and equipment, net		64,619		65,043
Deferred tax assets, net		241,171		364,493
Other assets		125,242		83,041
Intercompany receivables		0		0
Investments in subsidiaries		0		0
Total assets		5,142,666		4,977,086
Liabilities and stockholders’ equity
Accounts payable and accrued expenses		862,350		881,555
Mortgages and notes payable		1,747,704		1,748,747
Total Liabilities		2,610,054		2,630,302
Home Building [Member] | Reportable Legal Entities [Member] | KB Home Corporate [Member]
Assets
Cash and cash equivalents		649,859		357,966
Receivables		39,475		1,934
Inventories		0		0
Investments in unconsolidated joint ventures		0		0
Property and equipment, net		29,066		24,250
Deferred tax assets, net		83,027		96,301
Other assets		95,964		78,686
Intercompany receivables		3,486,621		3,624,081
Investments in subsidiaries		129,869		115,753
Total assets		897,391		559,137
Liabilities and stockholders’ equity
Accounts payable and accrued expenses		143,912		139,137
Mortgages and notes payable		1,716,974		1,715,748
Total Liabilities		1,860,886		1,854,885
Home Building [Member] | Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents		43,395		65,434
Receivables		166,454		181,047
Inventories		3,340,657		3,400,307
Investments in unconsolidated joint ventures		48,821		57,038
Property and equipment, net		32,337		37,539
Deferred tax assets, net		159,543		237,877
Other assets		22,625		2,666
Intercompany receivables		0		0
Investments in subsidiaries		0		0
Total assets		3,813,832		3,981,908
Liabilities and stockholders’ equity
Accounts payable and accrued expenses		434,064		453,929
Mortgages and notes payable		5,620		7,889
Total Liabilities		439,684		461,818
Home Building [Member] | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Assets
Cash and cash equivalents		28,779		30,414
Receivables		63,722		66,074
Inventories		330,472		304,295
Investments in unconsolidated joint ventures		0		0
Property and equipment, net		3,216		3,254
Deferred tax assets, net		(1,399)		30,315
Other assets		6,653		1,689
Intercompany receivables		213,647		186,022
Investments in subsidiaries		0		0
Total assets		431,443		436,041
Liabilities and stockholders’ equity
Accounts payable and accrued expenses		284,374		288,489
Mortgages and notes payable		25,110		25,110
Total Liabilities		309,484		313,599
Home Building [Member] | Consolidating Adjustments [Member]
Assets
Cash and cash equivalents		0		0
Receivables		0		0
Inventories		0		0
Investments in unconsolidated joint ventures		0		0
Property and equipment, net		0		0
Deferred tax assets, net		0		0
Other assets		0		0
Intercompany receivables		(3,700,268)		(3,810,103)
Investments in subsidiaries		(129,869)		(115,753)
Total assets		0		0
Liabilities and stockholders’ equity
Accounts payable and accrued expenses		0		0
Mortgages and notes payable		0		0
Total Liabilities		0		0
Financial Service [Member]
Assets
Cash and cash equivalents		1,093		1,044	$ 1,043
Receivables		1,414		2,232
Investments in unconsolidated joint ventures		10,298		14,374
Other assets	[1]	21,956		20,746
Total assets		34,761		38,396
Liabilities and stockholders’ equity
Accounts payable and accrued expenses		2,065		2,058
Financial services		2,065		2,058
Financial Service [Member] | Reportable Legal Entities [Member] | KB Home Corporate [Member]
Assets
Total assets		0		0
Liabilities and stockholders’ equity
Financial services		0		0
Financial Service [Member] | Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Assets
Total assets		0		0
Liabilities and stockholders’ equity
Financial services		0		0
Financial Service [Member] | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Assets
Total assets		34,761		38,396
Liabilities and stockholders’ equity
Financial services		2,065		2,058
Financial Service [Member] | Consolidating Adjustments [Member]
Assets
Total assets		0		0
Liabilities and stockholders’ equity
Financial services		$ 0		$ 0

[1] Other assets at August 31, 2020 and November 30, 2019 included $21.6 million and $20.6 million, respectively, of contract assets for estimated future renewal commissions related to then-existing insurance policies.