Supplemental Guarantor Information (Condensed Consolidating Balance Sheets) (Details) - USD ($) $ in Thousands	Nov. 30, 2019	Dec. 01, 2018	Nov. 30, 2018	Nov. 30, 2017	Nov. 30, 2016
Assets
Cash and cash equivalents	$ 454,858		$ 575,119	$ 720,861	$ 593,000
Receivables	249,055		292,830
Inventories	3,704,602		3,582,839
Property and equipment, net	65,043		24,283
Other Assets	83,041		83,100
Total assets	5,015,482		5,073,571
Liabilities and stockholders' equity
Notes payable	1,748,747		2,060,263
Due to Affiliate	0		0
Stockholder's equity	2,383,122		2,087,500	1,926,311	1,723,145
Total liabilities and Stockholders' equity	5,015,482		5,073,571
Consolidating Adjustments
Assets
Cash and cash equivalents	0		0	0	0
Total assets	(3,925,856)		(3,795,839)
Liabilities and stockholders' equity
Due to Affiliate	(3,810,103)		(3,728,182)
Stockholder's equity	(115,753)		(67,657)
Total liabilities and Stockholders' equity	(3,925,856)		(3,795,839)
Reportable Legal Entities [Member] | KB Home Corporate
Assets
Cash and cash equivalents	357,966		429,977	575,193	463,100
Total assets	4,298,971		4,252,493
Liabilities and stockholders' equity
Due to Affiliate	60,964		43,702
Stockholder's equity	2,383,122		2,087,500
Total liabilities and Stockholders' equity	4,298,971		4,252,493
Reportable Legal Entities [Member] | Guarantor Subsidiaries
Assets
Cash and cash equivalents	65,434		114,269	104,120	105,903
Total assets	3,981,908		4,002,279
Liabilities and stockholders' equity
Due to Affiliate	3,520,090		3,377,920
Stockholder's equity	0		0
Total liabilities and Stockholders' equity	3,981,908		4,002,279
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries
Assets
Cash and cash equivalents	31,458		30,873	$ 41,548	$ 23,997
Total assets	660,459		614,638
Liabilities and stockholders' equity
Due to Affiliate	229,049		306,560
Stockholder's equity	115,753		67,657
Total liabilities and Stockholders' equity	660,459		614,638
Homebuilding:
Assets
Cash and cash equivalents	453,814		574,359
Receivables	249,055		292,830
Inventories	3,704,602	$ 3,547,551	3,582,839
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	57,038		61,960
Property and equipment, net	65,043	55,477	24,283
Deferred tax assets, net	364,493	437,796	441,820
Other Assets	83,041		83,100
Total assets	4,977,086		5,061,191
Due from Affiliates	0		0
Investments in and Advances to Affiliates, Amount of Equity	0		0
Liabilities and stockholders' equity
Accounts payable, accrued expenses and other liabilities	881,555		924,313
Notes payable	1,748,747		2,060,263
Total Homebuilding	2,630,302		2,984,576
Homebuilding: | Consolidating Adjustments
Assets
Cash and cash equivalents	0		0
Receivables	0		0
Inventories	0		0
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	0		0
Property and equipment, net	0		0
Deferred tax assets, net	0		0
Other Assets	0		0
Total assets	0		0
Due from Affiliates	(3,810,103)		(3,728,182)
Investments in and Advances to Affiliates, Amount of Equity	(115,753)		(67,657)
Liabilities and stockholders' equity
Accounts payable, accrued expenses and other liabilities	0		0
Notes payable	0		0
Total Homebuilding	0		0
Homebuilding: | Reportable Legal Entities [Member] | KB Home Corporate
Assets
Cash and cash equivalents	357,966		429,977
Receivables	1,934		5,135
Inventories	0		0
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	0		0
Property and equipment, net	24,250		18,450
Deferred tax assets, net	96,301		84,564
Other Assets	78,686		77,288
Total assets	559,137		615,414
Due from Affiliates	3,624,081		3,569,422
Investments in and Advances to Affiliates, Amount of Equity	115,753		67,657
Liabilities and stockholders' equity
Accounts payable, accrued expenses and other liabilities	139,137		126,176
Notes payable	1,715,748		1,995,115
Total Homebuilding	1,854,885		2,121,291
Homebuilding: | Reportable Legal Entities [Member] | Guarantor Subsidiaries
Assets
Cash and cash equivalents	65,434		114,269
Receivables	181,047		198,465
Inventories	3,400,307		3,314,386
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	57,038		61,960
Property and equipment, net	37,539		5,522
Deferred tax assets, net	237,877		303,669
Other Assets	2,666		4,008
Total assets	3,981,908		4,002,279
Due from Affiliates	0		0
Investments in and Advances to Affiliates, Amount of Equity	0		0
Liabilities and stockholders' equity
Accounts payable, accrued expenses and other liabilities	453,929		584,321
Notes payable	7,889		40,038
Total Homebuilding	461,818		624,359
Homebuilding: | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries
Assets
Cash and cash equivalents	30,414		30,113
Receivables	66,074		89,230
Inventories	304,295		268,453
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	0		0
Property and equipment, net	3,254		311
Deferred tax assets, net	30,315		53,587
Other Assets	1,689		1,804
Total assets	436,041		443,498
Due from Affiliates	186,022		158,760
Investments in and Advances to Affiliates, Amount of Equity	0		0
Liabilities and stockholders' equity
Accounts payable, accrued expenses and other liabilities	288,489		213,816
Notes payable	25,110		25,110
Total Homebuilding	313,599		238,926
Financial services
Assets
Cash and cash equivalents	1,044		760
Receivables	2,232		2,885
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	14,374		8,594
Other Assets	20,746		141
Total assets	38,396	$ 32,108	12,380
Liabilities and stockholders' equity
Accounts payable, accrued expenses and other liabilities	2,058		1,495
Financial services	2,058		1,495
Financial services | Consolidating Adjustments
Assets
Total assets	0		0
Liabilities and stockholders' equity
Financial services	0		0
Financial services | Reportable Legal Entities [Member] | KB Home Corporate
Assets
Total assets	0		0
Liabilities and stockholders' equity
Financial services	0		0
Financial services | Reportable Legal Entities [Member] | Guarantor Subsidiaries
Assets
Total assets	0		0
Liabilities and stockholders' equity
Financial services	0		0
Financial services | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries
Assets
Total assets	38,396		12,380
Liabilities and stockholders' equity
Financial services	$ 2,058		$ 1,495