Supplemental Guarantor Information (Condensed Consolidated Statements of Operations) (Details) - USD ($) $ in Thousands	3 Months Ended
	Feb. 28, 2019	Feb. 28, 2018
Condensed Consolidated Statements of Operations
Total revenues	$ 811,483	$ 871,623
Homebuilding:
Equity in income of unconsolidated joint ventures	396	(426)
Total pretax income	34,511	46,045
Income tax expense	(4,500)	(117,300)
Equity in net income of subsidiaries	0	0
Net income (loss)	30,011	(71,255)
Reportable Legal Entities [Member] | KB Home Corporate [Member]
Condensed Consolidated Statements of Operations
Total revenues	0	0
Homebuilding:
Total pretax income	20,409	13,706
Income tax expense	(700)	(44,700)
Equity in net income of subsidiaries	10,302	(40,261)
Net income (loss)	30,011	(71,255)
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Condensed Consolidated Statements of Operations
Total revenues	744,453	794,689
Homebuilding:
Total pretax income	15,407	30,993
Income tax expense	(3,400)	(48,100)
Equity in net income of subsidiaries	0	0
Net income (loss)	12,007	(17,107)
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Consolidated Statements of Operations
Total revenues	67,030	76,934
Homebuilding:
Total pretax income	(1,305)	1,346
Income tax expense	(400)	(24,500)
Equity in net income of subsidiaries	0	0
Net income (loss)	(1,705)	(23,154)
Consolidating Adjustments [Member]
Condensed Consolidated Statements of Operations
Total revenues	0	0
Homebuilding:
Total pretax income	0	0
Income tax expense	0	0
Equity in net income of subsidiaries	(10,302)	40,261
Net income (loss)	(10,302)	40,261
Home Building [Member]
Condensed Consolidated Statements of Operations
Total revenues	808,788	869,205
Homebuilding:
Construction and land costs	(670,855)	(729,478)
Selling, general and administrative expenses	(106,594)	(95,724)
Operating income	31,339	44,003
Interest income	1,105	1,003
Interest expense	0	0
Intercompany interest	0	0
Equity in income of unconsolidated joint ventures	(406)	(845)
Total pretax income	32,038	44,161
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	(25,382)	(22,166)
Operating income	(25,382)	(22,166)
Interest income	1,014	998
Interest expense	(33,195)	(37,972)
Intercompany interest	77,972	72,846
Equity in income of unconsolidated joint ventures	0	0
Total pretax income	20,409	13,706
Home Building [Member] | Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Condensed Consolidated Statements of Operations
Total revenues	744,453	794,689
Homebuilding:
Construction and land costs	(611,041)	(664,096)
Selling, general and administrative expenses	(75,540)	(67,117)
Operating income	57,872	63,476
Interest income	0	5
Interest expense	(321)	(689)
Intercompany interest	(41,738)	(30,954)
Equity in income of unconsolidated joint ventures	(406)	(845)
Total pretax income	15,407	30,993
Home Building [Member] | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Consolidated Statements of Operations
Total revenues	64,335	74,516
Homebuilding:
Construction and land costs	(59,814)	(65,382)
Selling, general and administrative expenses	(5,672)	(6,441)
Operating income	(1,151)	2,693
Interest income	91	0
Interest expense	(1,272)	(1,283)
Intercompany interest	(1,446)	(1,948)
Equity in income of unconsolidated joint ventures	0	0
Total pretax income	(3,778)	(538)
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	34,788	39,944
Intercompany interest	(34,788)	(39,944)
Equity in income of unconsolidated joint ventures	0	0
Total pretax income	0	0
Financial Service [Member]
Condensed Consolidated Statements of Operations
Total revenues	2,695	2,418
Homebuilding:
Selling, general and administrative expenses	(1,024)	(953)
Operating income	1,671	1,465
Equity in income of unconsolidated joint ventures	802	419
Total pretax income	2,473	1,884
Financial Service [Member] | Reportable Legal Entities [Member] | KB Home Corporate [Member]
Homebuilding:
Total pretax income	0	0
Financial Service [Member] | Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Homebuilding:
Total pretax income	0	0
Financial Service [Member] | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Homebuilding:
Total pretax income	2,473	1,884
Financial Service [Member] | Consolidating Adjustments [Member]
Homebuilding:
Total pretax income	$ 0	$ 0