Supplemental Guarantor Information (Condensed Consolidated Statements of Operations) (Details) - USD ($) $ in Thousands	3 Months Ended
	Feb. 29, 2020	Feb. 28, 2019
Condensed Consolidated Statements of Operations
Total revenues	$ 1,075,935	$ 811,483
Homebuilding:
Equity in income of unconsolidated joint ventures	5,127	396
Total pretax income (loss)	68,848	34,511
Income tax expense	(9,100)	(4,500)
Equity in net income of subsidiaries	0	0
Net income	59,748	30,011
Reportable Legal Entities [Member] | KB Home Corporate [Member]
Condensed Consolidated Statements of Operations
Total revenues	0	0
Homebuilding:
Total pretax income (loss)	24,259	20,409
Income tax expense	(3,100)	(700)
Equity in net income of subsidiaries	38,589	10,302
Net income	59,748	30,011
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Condensed Consolidated Statements of Operations
Total revenues	992,545	744,453
Homebuilding:
Total pretax income (loss)	40,044	15,407
Income tax expense	(5,100)	(3,400)
Equity in net income of subsidiaries	0	0
Net income	34,944	12,007
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Consolidated Statements of Operations
Total revenues	83,390	67,030
Homebuilding:
Total pretax income (loss)	4,545	(1,305)
Income tax expense	(900)	(400)
Equity in net income of subsidiaries	0	0
Net income	3,645	(1,705)
Consolidating Adjustments [Member]
Condensed Consolidated Statements of Operations
Total revenues	0	0
Homebuilding:
Total pretax income (loss)	0	0
Income tax expense	0	0
Equity in net income of subsidiaries	(38,589)	(10,302)
Net income	(38,589)	(10,302)
Home Building [Member]
Condensed Consolidated Statements of Operations
Total revenues	1,072,382	808,788
Homebuilding:
Construction and land costs	(886,053)	(670,855)
Selling, general and administrative expenses	(126,134)	(106,594)
Operating income	60,195	31,339
Interest income	935	1,105
Interest expense	0	0
Intercompany interest	0	0
Equity in income of unconsolidated joint ventures	1,905	(406)
Total pretax income (loss)	63,035	32,038
Home Building [Member] | Reportable Legal Entities [Member] | KB Home Corporate [Member]
Condensed Consolidated Statements of Operations
Total revenues	0	0
Homebuilding:
Construction and land costs	0	0
Selling, general and administrative expenses	(27,650)	(25,382)
Operating income	(27,650)	(25,382)
Interest income	884	1,014
Interest expense	(29,555)	(33,195)
Intercompany interest	80,580	77,972
Equity in income of unconsolidated joint ventures	0	0
Total pretax income (loss)	24,259	20,409
Home Building [Member] | Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Condensed Consolidated Statements of Operations
Total revenues	992,545	744,453
Homebuilding:
Construction and land costs	(815,558)	(611,041)
Selling, general and administrative expenses	(93,012)	(75,540)
Operating income	83,975	57,872
Interest income	0	0
Interest expense	0	(321)
Intercompany interest	(45,836)	(41,738)
Equity in income of unconsolidated joint ventures	1,905	(406)
Total pretax income (loss)	40,044	15,407
Home Building [Member] | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Consolidated Statements of Operations
Total revenues	79,837	64,335
Homebuilding:
Construction and land costs	(70,495)	(59,814)
Selling, general and administrative expenses	(5,472)	(5,672)
Operating income	3,870	(1,151)
Interest income	51	91
Interest expense	(1,407)	(1,272)
Intercompany interest	(3,782)	(1,446)
Equity in income of unconsolidated joint ventures	0	0
Total pretax income (loss)	(1,268)	(3,778)
Home Building [Member] | Consolidating Adjustments [Member]
Condensed Consolidated Statements of Operations
Total revenues	0	0
Homebuilding:
Construction and land costs	0	0
Selling, general and administrative expenses	0	0
Operating income	0	0
Interest income	0	0
Interest expense	30,962	34,788
Intercompany interest	(30,962)	(34,788)
Equity in income of unconsolidated joint ventures	0	0
Total pretax income (loss)	0	0
Financial Service [Member]
Condensed Consolidated Statements of Operations
Total revenues	3,553	2,695
Homebuilding:
Selling, general and administrative expenses	(962)	(1,024)
Operating income	2,591	1,671
Equity in income of unconsolidated joint ventures	3,222	802
Total pretax income (loss)	5,813	2,473
Financial Service [Member] | Reportable Legal Entities [Member] | KB Home Corporate [Member]
Homebuilding:
Total pretax income (loss)	0	0
Financial Service [Member] | Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Homebuilding:
Total pretax income (loss)	0	0
Financial Service [Member] | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Homebuilding:
Total pretax income (loss)	5,813	2,473
Financial Service [Member] | Consolidating Adjustments [Member]
Homebuilding:
Total pretax income (loss)	$ 0	$ 0