Supplemental Guarantor Information (Condensed Consolidated Statements of Cash Flows) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Feb. 28, 2019	Nov. 30, 2019	Nov. 30, 2018	Nov. 30, 2017
Condensed Consolidated Statements of Cash Flows
Net cash provided by (used in) operating activities		$ 251,042	$ 221,512	$ 513,219
Cash flows from investing activities:
Contributions to unconsolidated joint ventures		(11,290)	(22,671)	(18,694)
Return of investments in unconsolidated joint ventures		5,001	9,934	11,035
Proceeds from Sale of Buildings	$ 5,800	5,804	0	0
Purchases of property and equipment, net		(40,459)	(7,370)	(8,085)
Intercompany		0	0	0
Net cash used in investing activities		(40,944)	(20,107)	(15,744)
Proceeds from Issuance of Senior Long-term Debt		705,250	0	0
Cash flows from financing activities:
Issuance costs for unsecured revolving credit facility		(11,128)	0	(1,711)
Repayment of senior notes		(986,231)	(300,000)	(270,326)
Borrowings under revolving credit facility		610,000	70,000	0
Repayments under revolving credit facility		(610,000)	(70,000)	0
Payments on mortgages and land contracts due to land sellers and other loans		(41,116)	(14,751)	(106,382)
Issuance of common stock under employee stock plans		30,524	20,011	23,162
Excess Tax Benefit (Tax Deficiency) from Share-based Compensation, Financing Activities		0	0	958
Payments of cash dividends		(20,370)	(8,892)	(8,642)
Tax payments associated with stock-based compensation awards		(7,288)	(8,476)	(6,673)
Payments for Repurchase of Common Stock		0	(35,039)	0
Intercompany		0	0	0
Net cash used in financing activities		(330,359)	(347,147)	(369,614)
Net increase (decrease) in cash and cash equivalents		(120,261)	(145,742)	127,861
Cash and cash equivalents at beginning of year	575,119	575,119	720,861	593,000
Cash and cash equivalents at end of year		454,858	575,119	720,861
Consolidating Adjustments
Condensed Consolidated Statements of Cash Flows
Net cash provided by (used in) operating activities		0	0	0
Cash flows from investing activities:
Contributions to unconsolidated joint ventures		0	0	0
Return of investments in unconsolidated joint ventures		0	0	0
Proceeds from Sale of Buildings		0
Purchases of property and equipment, net		0	0	0
Intercompany		(105,055)	43,128	(311,857)
Net cash used in investing activities		(105,055)	43,128	(311,857)
Proceeds from Issuance of Senior Long-term Debt		0
Cash flows from financing activities:
Issuance costs for unsecured revolving credit facility		0		0
Repayment of senior notes		0	0	0
Borrowings under revolving credit facility		0	0
Repayments under revolving credit facility		0	0
Payments on mortgages and land contracts due to land sellers and other loans		0	0	0
Issuance of common stock under employee stock plans		0	0	0
Excess Tax Benefit (Tax Deficiency) from Share-based Compensation, Financing Activities				0
Payments of cash dividends		0	0	0
Tax payments associated with stock-based compensation awards		0	0	0
Payments for Repurchase of Common Stock			0
Intercompany		105,055	(43,128)	311,857
Net cash used in financing activities		105,055	(43,128)	311,857
Net increase (decrease) in cash and cash equivalents		0	0	0
Cash and cash equivalents at beginning of year	0	0	0	0
Cash and cash equivalents at end of year		0	0	0
Reportable Legal Entities [Member] | KB Home Corporate
Condensed Consolidated Statements of Cash Flows
Net cash provided by (used in) operating activities		118,542	236,892	70,683
Cash flows from investing activities:
Contributions to unconsolidated joint ventures		0	0	0
Return of investments in unconsolidated joint ventures		0	0	0
Proceeds from Sale of Buildings		0
Purchases of property and equipment, net		(6,365)	(6,584)	(7,215)
Intercompany		105,055	(43,128)	311,857
Net cash used in investing activities		98,690	(49,712)	304,642
Proceeds from Issuance of Senior Long-term Debt		705,250
Cash flows from financing activities:
Issuance costs for unsecured revolving credit facility		(11,128)		(1,711)
Repayment of senior notes		(986,231)	(300,000)	(270,326)
Borrowings under revolving credit facility		610,000	70,000
Repayments under revolving credit facility		(610,000)	(70,000)
Payments on mortgages and land contracts due to land sellers and other loans		0	0	0
Issuance of common stock under employee stock plans		30,524	20,011	23,162
Excess Tax Benefit (Tax Deficiency) from Share-based Compensation, Financing Activities				958
Payments of cash dividends		(20,370)	(8,892)	(8,642)
Tax payments associated with stock-based compensation awards		(7,288)	(8,476)	(6,673)
Payments for Repurchase of Common Stock			(35,039)
Intercompany		0	0	0
Net cash used in financing activities		(289,243)	(332,396)	(263,232)
Net increase (decrease) in cash and cash equivalents		(72,011)	(145,216)	112,093
Cash and cash equivalents at beginning of year	429,977	429,977	575,193	463,100
Cash and cash equivalents at end of year		357,966	429,977	575,193
Reportable Legal Entities [Member] | Guarantor Subsidiaries
Condensed Consolidated Statements of Cash Flows
Net cash provided by (used in) operating activities		32,864	9,668	366,005
Cash flows from investing activities:
Contributions to unconsolidated joint ventures		(11,290)	(22,672)	(13,569)
Return of investments in unconsolidated joint ventures		5,001	9,934	4,119
Proceeds from Sale of Buildings		5,804
Purchases of property and equipment, net		(23,618)	(674)	(809)
Intercompany		0	0	0
Net cash used in investing activities		(24,103)	(13,412)	(10,259)
Proceeds from Issuance of Senior Long-term Debt		0
Cash flows from financing activities:
Issuance costs for unsecured revolving credit facility		0		0
Repayment of senior notes		0	0	0
Borrowings under revolving credit facility		0	0
Repayments under revolving credit facility		0	0
Payments on mortgages and land contracts due to land sellers and other loans		(41,116)	(13,831)	(106,382)
Issuance of common stock under employee stock plans		0	0	0
Excess Tax Benefit (Tax Deficiency) from Share-based Compensation, Financing Activities				0
Payments of cash dividends		0	0	0
Tax payments associated with stock-based compensation awards		0	0	0
Payments for Repurchase of Common Stock			0
Intercompany		(16,480)	27,724	(251,147)
Net cash used in financing activities		(57,596)	13,893	(357,529)
Net increase (decrease) in cash and cash equivalents		(48,835)	10,149	(1,783)
Cash and cash equivalents at beginning of year	114,269	114,269	104,120	105,903
Cash and cash equivalents at end of year		65,434	114,269	104,120
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries
Condensed Consolidated Statements of Cash Flows
Net cash provided by (used in) operating activities		99,636	(25,048)	76,531
Cash flows from investing activities:
Contributions to unconsolidated joint ventures		0	1	(5,125)
Return of investments in unconsolidated joint ventures		0	0	6,916
Proceeds from Sale of Buildings		0
Purchases of property and equipment, net		(10,476)	(112)	(61)
Intercompany		0	0	0
Net cash used in investing activities		(10,476)	(111)	1,730
Proceeds from Issuance of Senior Long-term Debt		0
Cash flows from financing activities:
Issuance costs for unsecured revolving credit facility		0		0
Repayment of senior notes		0	0	0
Borrowings under revolving credit facility		0	0
Repayments under revolving credit facility		0	0
Payments on mortgages and land contracts due to land sellers and other loans		0	(920)	0
Issuance of common stock under employee stock plans		0	0	0
Excess Tax Benefit (Tax Deficiency) from Share-based Compensation, Financing Activities				0
Payments of cash dividends		0	0	0
Tax payments associated with stock-based compensation awards		0	0	0
Payments for Repurchase of Common Stock			0
Intercompany		(88,575)	15,404	(60,710)
Net cash used in financing activities		(88,575)	14,484	(60,710)
Net increase (decrease) in cash and cash equivalents		585	(10,675)	17,551
Cash and cash equivalents at beginning of year	$ 30,873	30,873	41,548	23,997
Cash and cash equivalents at end of year		$ 31,458	$ 30,873	$ 41,548