Supplemental Guarantor Information (Condensed Consolidating Statements of Operations) (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Nov. 30, 2018	Aug. 31, 2018	May 31, 2018	Feb. 28, 2018	Nov. 30, 2017	Aug. 31, 2017	May 31, 2017	Feb. 28, 2017	Nov. 30, 2018	Nov. 30, 2017	Nov. 30, 2016
Condensed Consolidated Statements of Operations
Revenues		$ 1,348,609	$ 1,225,347	$ 1,101,423	$ 871,623	$ 1,403,138	$ 1,144,001	$ 1,002,794	$ 818,596	$ 4,547,002	$ 4,368,529	$ 3,594,646
Homebuilding:
Revenues										4,533,795	4,356,265	3,582,943
Construction and land costs										(3,743,920)	(3,646,468)	(3,041,101)
Selling, general and administrative expenses										(444,154)	(426,394)	(389,441)
Operating income										345,721	283,403	152,401
Interest income										3,514	1,240	529
Interest Expense	[1]									0	(6,307)	(5,900)
Intercompany Interest Income (Expense)										0	0	0
Equity in income (loss) of unconsolidated joint ventures										9,367	2,825	(5,601)
Pretax income (loss)		128,936	114,676	78,308	46,045	137,346	79,208	51,982	21,459	367,965	289,995	149,315
Income tax expense										(197,600)	(109,400)	(43,700)
Income (Loss) from Subsidiaries, Net of Tax										0	0	0
Net income		$ 96,836	$ 87,476	$ 57,308	$ (71,255)	$ 84,346	$ 50,208	$ 31,782	$ 14,259	170,365	180,595	105,615
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										(101,152)	(91,120)	(91,859)
Operating income										(101,152)	(91,120)	(91,859)
Interest income										3,273	1,232	470
Interest Expense										(141,812)	(172,102)	(177,329)
Intercompany Interest Income (Expense)										302,253	266,784	301,432
Pretax income (loss)										62,562	4,794	32,714
Income tax expense										(62,100)	(8,800)	17,200
Income (Loss) from Subsidiaries, Net of Tax										169,903	184,601	55,701
Net income										170,365	180,595	105,615
Guarantor Subsidiaries
Condensed Consolidated Statements of Operations
Revenues										4,198,969	4,034,057	3,243,928
Homebuilding:
Revenues										4,198,969	4,034,057	3,243,928
Construction and land costs										(3,435,058)	(3,342,617)	(2,706,402)
Selling, general and administrative expenses										(311,815)	(298,498)	(254,210)
Operating income										452,096	392,942	283,316
Interest income										11	8	55
Interest Expense										(2,624)	(1,635)	(3,958)
Intercompany Interest Income (Expense)										(142,882)	(118,138)	(105,865)
Pretax income (loss)										308,667	271,770	171,367
Income tax expense										(101,200)	(100,000)	(52,700)
Income (Loss) from Subsidiaries, Net of Tax										0	0	0
Net income										207,467	171,770	118,667
Non-Guarantor Subsidiaries
Condensed Consolidated Statements of Operations
Revenues										348,033	334,472	350,718
Homebuilding:
Revenues										334,826	322,208	339,015
Construction and land costs										(308,862)	(303,851)	(334,699)
Selling, general and administrative expenses										(31,187)	(36,776)	(43,372)
Operating income										(5,223)	(18,419)	(39,056)
Interest income										230	0	4
Interest Expense										(5,262)	(3,434)	(3,946)
Intercompany Interest Income (Expense)										(9,673)	22,218	(16,234)
Pretax income (loss)										(3,264)	13,431	(54,766)
Income tax expense										(34,300)	(600)	(8,200)
Income (Loss) from Subsidiaries, Net of Tax										0	0	0
Net income										(37,564)	12,831	(62,966)
Homebuilding [Member]
Homebuilding:
Equity in income (loss) of unconsolidated joint ventures										2,066	(1,409)	(2,181)
Pretax income (loss)										351,301	276,927	144,849
Homebuilding [Member] | KB Home Corporate
Homebuilding:
Equity in income (loss) of unconsolidated joint ventures										0	0	0
Pretax income (loss)										62,562	4,794	32,714
Homebuilding [Member] | Guarantor Subsidiaries
Homebuilding:
Equity in income (loss) of unconsolidated joint ventures										2,066	(1,407)	(2,181)
Pretax income (loss)										308,667	271,770	171,367
Homebuilding [Member] | Non-Guarantor Subsidiaries
Homebuilding:
Equity in income (loss) of unconsolidated joint ventures										0	(2)	0
Pretax income (loss)										(19,928)	363	(59,232)
Financial services [Member]
Homebuilding:
Operating income										9,363	8,834	7,886
Equity in income (loss) of unconsolidated joint ventures										7,301	4,234	(3,420)
Pretax income (loss)										16,664	13,068	4,466
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)										16,664	13,068	4,466
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										149,698	170,864	179,333
Intercompany Interest Income (Expense)										(149,698)	(170,864)	(179,333)
Pretax income (loss)										0	0	0
Income tax expense										0	0	0
Income (Loss) from Subsidiaries, Net of Tax										(169,903)	(184,601)	(55,701)
Net income										(169,903)	(184,601)	(55,701)
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.