Supplemental Guarantor Information (Condensed Consolidating Statements of Operations) (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Nov. 30, 2017	Aug. 31, 2017	May 31, 2017	Feb. 28, 2017	Nov. 30, 2016	Aug. 31, 2016	May 31, 2016	Feb. 29, 2016	Nov. 30, 2017	Nov. 30, 2016	Nov. 30, 2015
Condensed Consolidated Statements of Operations
Revenues		$ 1,403,138	$ 1,144,001	$ 1,002,794	$ 818,596	$ 1,191,942	$ 913,283	$ 811,050	$ 678,371	$ 4,368,529	$ 3,594,646	$ 3,032,030
Homebuilding:
Revenues										4,356,265	3,582,943	3,020,987
Construction and land costs										(3,646,468)	(3,041,101)	(2,539,368)
Selling, general and administrative expenses										(426,394)	(389,441)	(342,998)
Operating income										283,403	152,401	138,621
Interest income										1,240	529	458
Interest Expense	[1]									(6,307)	(5,900)	(21,856)
Intercompany Interest Income (Expense)										0	0	0
Equity in income (loss) of unconsolidated joint ventures										2,825	(5,601)	2,488
Pretax income (loss)		137,346	79,208	51,982	21,459	55,028	53,463	24,797	16,027	289,995	149,315	127,043
Income tax expense										(109,400)	(43,700)	(42,400)
Income (Loss) from Subsidiaries, Net of Tax										0	0	0
Net income		$ 84,346	$ 50,208	$ 31,782	$ 14,259	$ 37,528	$ 39,363	$ 15,597	$ 13,127	180,595	105,615	84,643
KB Home Corporate
Condensed Consolidated Statements of Operations
Revenues										0	0	0
Homebuilding:
Revenues										0	0	0
Construction and land costs										0	0	0
Selling, general and administrative expenses										(91,120)	(91,859)	(86,053)
Operating income										(91,120)	(91,859)	(86,053)
Interest income										1,232	470	451
Interest Expense										(172,102)	(177,329)	(180,701)
Intercompany Interest Income (Expense)										266,784	301,432	289,727
Pretax income (loss)										4,794	32,714	23,424
Income tax expense										(8,800)	17,200	2,000
Income (Loss) from Subsidiaries, Net of Tax										184,601	55,701	59,219
Net income										180,595	105,615	84,643
Guarantor Subsidiaries
Condensed Consolidated Statements of Operations
Revenues										3,957,267	3,169,545	2,640,678
Homebuilding:
Revenues										3,957,267	3,169,545	2,640,678
Construction and land costs										(3,286,891)	(2,661,888)	(2,196,228)
Selling, general and administrative expenses										(293,233)	(251,384)	(213,292)
Operating income										377,143	256,273	231,158
Interest income										8	55	6
Interest Expense										(1,635)	(3,958)	(6,184)
Intercompany Interest Income (Expense)										(117,926)	(107,388)	(101,540)
Pretax income (loss)										256,183	142,803	121,637
Income tax expense										(100,000)	(52,700)	(46,700)
Income (Loss) from Subsidiaries, Net of Tax										0	0	0
Net income										156,183	90,103	74,937
Non-Guarantor Subsidiaries
Condensed Consolidated Statements of Operations
Revenues										411,262	425,101	391,352
Homebuilding:
Revenues										398,998	413,398	380,309
Construction and land costs										(359,577)	(379,213)	(343,140)
Selling, general and administrative expenses										(42,041)	(46,198)	(43,653)
Operating income										(2,620)	(12,013)	(6,484)
Interest income										0	4	1
Interest Expense										3,434	3,946	0
Intercompany Interest Income (Expense)										22,006	(14,711)	(23,158)
Pretax income (loss)										29,018	(26,202)	(18,018)
Income tax expense										(600)	(8,200)	2,300
Income (Loss) from Subsidiaries, Net of Tax										0	0	0
Net income										28,418	(34,402)	(15,718)
Homebuilding [Member]
Homebuilding:
Equity in income (loss) of unconsolidated joint ventures										(1,409)	(2,181)	(1,804)
Pretax income (loss)										276,927	144,849	115,419
Homebuilding [Member] | KB Home Corporate
Homebuilding:
Equity in income (loss) of unconsolidated joint ventures										0	0	0
Pretax income (loss)										4,794	32,714	23,424
Homebuilding [Member] | Guarantor Subsidiaries
Homebuilding:
Equity in income (loss) of unconsolidated joint ventures										(1,407)	(2,179)	(1,803)
Pretax income (loss)										256,183	142,803	121,637
Homebuilding [Member] | Non-Guarantor Subsidiaries
Homebuilding:
Equity in income (loss) of unconsolidated joint ventures										(2)	(2)	(1)
Pretax income (loss)										15,950	(30,668)	(29,642)
Financial services [Member]
Homebuilding:
Operating income										8,834	7,886	7,332
Equity in income (loss) of unconsolidated joint ventures										4,234	(3,420)	4,292
Pretax income (loss)										13,068	4,466	11,624
Financial services [Member] | KB Home Corporate
Homebuilding:
Pretax income (loss)										0	0	0
Financial services [Member] | Guarantor Subsidiaries
Homebuilding:
Pretax income (loss)										0	0	0
Financial services [Member] | Non-Guarantor Subsidiaries
Homebuilding:
Pretax income (loss)										13,068	4,466	11,624
Consolidating Adjustments
Condensed Consolidated Statements of Operations
Revenues										0	0	0
Homebuilding:
Revenues										0	0	0
Construction and land costs										0	0	0
Selling, general and administrative expenses										0	0	0
Operating income										0	0	0
Interest income										0	0	0
Interest Expense										170,864	179,333	165,029
Intercompany Interest Income (Expense)										(170,864)	(179,333)	(165,029)
Pretax income (loss)										0	0	0
Income tax expense										0	0	0
Income (Loss) from Subsidiaries, Net of Tax										(184,601)	(55,701)	(59,219)
Net income										(184,601)	(55,701)	(59,219)
Consolidating Adjustments | Homebuilding [Member]
Homebuilding:
Equity in income (loss) of unconsolidated joint ventures										0	0	0
Pretax income (loss)										0	0	0
Consolidating Adjustments | Financial services [Member]
Homebuilding:
Pretax income (loss)										$ 0	$ 0	$ 0

[1] Interest incurred and interest expensed for the year ended November 30, 2017 included a charge of $5.7 million for the early extinguishment of debt.