Supplemental Guarantor Information (Condensed Consolidated Statements of Operations) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Aug. 31, 2020	Aug. 31, 2019	Aug. 31, 2020	Aug. 31, 2019
Condensed Consolidated Statements of Operations
Total revenues	$ 999,013	$ 1,160,786	$ 2,988,918	$ 2,994,072
Homebuilding:
Equity in income of unconsolidated joint ventures			26,855	5,859
Total pretax income	101,315	91,936	237,952	183,208
Income tax expense	(22,900)	(23,800)	(47,800)	(37,600)
Equity in net income of subsidiaries	0	0	0	0
Net income	78,415	68,136	190,152	145,608
Reportable Legal Entities [Member] | KB Home Corporate [Member]
Condensed Consolidated Statements of Operations
Total revenues	0	0	0	0
Homebuilding:
Total pretax income	26,755	26,913	77,078	67,369
Income tax expense	(6,700)	(6,900)	(16,500)	(10,400)
Equity in net income of subsidiaries	58,360	48,123	129,574	88,639
Net income	78,415	68,136	190,152	145,608
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Condensed Consolidated Statements of Operations
Total revenues	908,657	1,061,698	2,735,339	2,739,096
Homebuilding:
Total pretax income	61,259	60,224	137,479	111,850
Income tax expense	(13,300)	(14,900)	(26,200)	(21,300)
Equity in net income of subsidiaries	0	0	0	0
Net income	47,959	45,324	111,279	90,550
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Consolidated Statements of Operations
Total revenues	90,356	99,088	253,579	254,976
Homebuilding:
Total pretax income	13,301	4,799	23,395	3,989
Income tax expense	(2,900)	(2,000)	(5,100)	(5,900)
Equity in net income of subsidiaries	0	0	0	0
Net income	10,401	2,799	18,295	(1,911)
Consolidating Adjustments [Member]
Condensed Consolidated Statements of Operations
Total revenues	0	0	0	0
Homebuilding:
Total pretax income	0	0	0	0
Income tax expense	0	0	0	0
Equity in net income of subsidiaries	(58,360)	(48,123)	(129,574)	(88,639)
Net income	(58,360)	(48,123)	(129,574)	(88,639)
Home Building [Member]
Condensed Consolidated Statements of Operations
Total revenues	995,148	1,156,855	2,977,810	2,984,314
Homebuilding:
Construction and land costs	(798,495)	(943,754)	(2,429,001)	(2,458,353)
Selling, general and administrative expenses	(107,710)	(127,626)	(348,082)	(357,048)
Operating income	88,943	85,475	200,727	168,913
Interest income	786	201	2,163	1,745
Interest expense	0	0	0	0
Intercompany interest	0	0	0	0
Equity in income of unconsolidated joint ventures	1,922	(384)	11,981	(1,159)
Total pretax income	91,651	85,292	214,871	169,499
Home Building [Member] | Reportable Legal Entities [Member] | KB Home Corporate [Member]
Condensed Consolidated Statements of Operations
Total revenues	0	0	0	0
Homebuilding:
Construction and land costs	0	0	0	0
Selling, general and administrative expenses	(22,699)	(23,619)	(75,129)	(76,507)
Operating income	(22,699)	(23,619)	(75,129)	(76,507)
Interest income	784	140	2,075	1,549
Interest expense	(29,552)	(34,488)	(88,648)	(102,763)
Intercompany interest	78,222	84,880	238,780	245,090
Equity in income of unconsolidated joint ventures	0	0	0	0
Total pretax income	26,755	26,913	77,078	67,369
Home Building [Member] | Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Condensed Consolidated Statements of Operations
Total revenues	908,657	1,061,698	2,735,339	2,739,096
Homebuilding:
Construction and land costs	(725,215)	(859,733)	(2,218,683)	(2,226,829)
Selling, general and administrative expenses	(80,978)	(95,376)	(257,460)	(268,506)
Operating income	102,464	106,589	259,196	243,761
Interest income	0	20	12	20
Interest expense	(15)	(175)	(73)	(630)
Intercompany interest	(43,112)	(45,826)	(133,637)	(130,142)
Equity in income of unconsolidated joint ventures	1,922	(384)	11,981	(1,159)
Total pretax income	61,259	60,224	137,479	111,850
Home Building [Member] | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Consolidated Statements of Operations
Total revenues	86,491	95,157	242,471	245,218
Homebuilding:
Construction and land costs	(73,280)	(84,021)	(210,318)	(231,524)
Selling, general and administrative expenses	(4,033)	(8,631)	(15,493)	(12,035)
Operating income	9,178	2,505	16,660	1,659
Interest income	2	41	76	176
Interest expense	(1,487)	(1,361)	(4,350)	(3,963)
Intercompany interest	(4,056)	(3,030)	(12,072)	(7,592)
Equity in income of unconsolidated joint ventures	0	0	0	0
Total pretax income	3,637	(1,845)	314	(9,720)
Home Building [Member] | Consolidating Adjustments [Member]
Condensed Consolidated Statements of Operations
Total revenues	0	0	0	0
Homebuilding:
Construction and land costs	0	0	0	0
Selling, general and administrative expenses	0	0	0	0
Operating income	0	0	0	0
Interest income	0	0	0	0
Interest expense	31,054	36,024	93,071	107,356
Intercompany interest	(31,054)	(36,024)	(93,071)	(107,356)
Equity in income of unconsolidated joint ventures	0	0	0	0
Total pretax income	0	0	0	0
Financial Service [Member]
Condensed Consolidated Statements of Operations
Total revenues	3,865	3,931	11,108	9,758
Homebuilding:
Selling, general and administrative expenses	(1,056)	(1,003)	(2,901)	(3,067)
Operating income	2,809	2,928	8,207	6,691
Equity in income of unconsolidated joint ventures	6,855	3,716	14,874	7,018
Total pretax income	9,664	6,644	23,081	13,709
Financial Service [Member] | Reportable Legal Entities [Member] | KB Home Corporate [Member]
Homebuilding:
Total pretax income	0	0	0	0
Financial Service [Member] | Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Homebuilding:
Total pretax income	0	0	0	0
Financial Service [Member] | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Homebuilding:
Total pretax income	9,664	6,644	23,081	13,709
Financial Service [Member] | Consolidating Adjustments [Member]
Homebuilding:
Total pretax income	$ 0	$ 0	$ 0	$ 0