Supplemental Guarantor Information (Condensed Consolidated Statements of Cash Flows) (Details) - USD ($) $ in Thousands	9 Months Ended
	Aug. 31, 2020	Aug. 31, 2019
Cash flows from operating activities:
Net cash provided by operating activities	$ 329,211	$ (152,144)
Cash flows from investing activities:
Contributions to unconsolidated joint ventures	(6,048)	(7,656)
Return of investments in unconsolidated joint ventures	8,816	5,001
Proceeds from sale of building	0	5,804
Purchases of property and equipment, net	(21,154)	(32,211)
Intercompany	0	0
Net cash used in investing activities	(18,386)	(29,062)
Cash flows from financing activities:
Proceeds from issuance of debt	0	405,250
Issuance costs for unsecured revolving credit facility	0	(5,209)
Repayment of senior notes	0	(630,000)
Borrowings under revolving credit facility	0	460,000
Repayments under revolving credit facility	0	(410,000)
Payments on mortgages and land contracts due to land sellers and other loans	(20,314)	(32,149)
Issuance of common stock under employee stock plans	8,404	18,729
Payments of cash dividends	(24,428)	(12,352)
Tax payments associated with stock-based compensation awards	(6,219)	(3,345)
Intercompany	0	0
Net cash used in financing activities	(42,557)	(209,076)
Net increase (decrease) in cash and cash equivalents	268,268	(390,282)
Cash and cash equivalents at beginning of period	454,858	575,119
Cash and cash equivalents at end of period	723,126	184,837
Guarantor Subsidiaries [Member]
Cash flows from financing activities:
Proceeds from issuance of debt		0
Issuance costs for unsecured revolving credit facility		0
Non-Guarantor Subsidiaries [Member]
Cash flows from financing activities:
Proceeds from issuance of debt		0
Issuance costs for unsecured revolving credit facility		0
Reportable Legal Entities [Member] | KB Home Corporate [Member]
Cash flows from operating activities:
Net cash provided by operating activities	62,684	92,935
Cash flows from investing activities:
Contributions to unconsolidated joint ventures	0	0
Return of investments in unconsolidated joint ventures	0	0
Proceeds from sale of building		0
Purchases of property and equipment, net	(5,148)	(4,728)
Intercompany	256,600	(274,010)
Net cash used in investing activities	251,452	(278,738)
Cash flows from financing activities:
Proceeds from issuance of debt		405,250
Issuance costs for unsecured revolving credit facility		(5,209)
Repayment of senior notes		(630,000)
Borrowings under revolving credit facility		460,000
Repayments under revolving credit facility		(410,000)
Payments on mortgages and land contracts due to land sellers and other loans	0	0
Issuance of common stock under employee stock plans	8,404	18,729
Payments of cash dividends	(24,428)	(12,352)
Tax payments associated with stock-based compensation awards	(6,219)	(3,345)
Intercompany	0	0
Net cash used in financing activities	(22,243)	(176,927)
Net increase (decrease) in cash and cash equivalents	291,893	(362,730)
Cash and cash equivalents at beginning of period	357,966	429,977
Cash and cash equivalents at end of period	649,859	67,247
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Cash flows from operating activities:
Net cash provided by operating activities	253,483	(335,428)
Cash flows from investing activities:
Contributions to unconsolidated joint ventures	(6,048)	(7,656)
Return of investments in unconsolidated joint ventures	8,816	5,001
Proceeds from sale of building		5,804
Purchases of property and equipment, net	(12,344)	(18,252)
Intercompany	0	0
Net cash used in investing activities	(9,576)	(15,103)
Cash flows from financing activities:
Repayment of senior notes		0
Borrowings under revolving credit facility		0
Repayments under revolving credit facility		0
Payments on mortgages and land contracts due to land sellers and other loans	(20,314)	(32,149)
Issuance of common stock under employee stock plans	0	0
Payments of cash dividends	0	0
Tax payments associated with stock-based compensation awards	0	0
Intercompany	(245,632)	372,454
Net cash used in financing activities	(265,946)	340,305
Net increase (decrease) in cash and cash equivalents	(22,039)	(10,226)
Cash and cash equivalents at beginning of period	65,434	114,269
Cash and cash equivalents at end of period	43,395	104,043
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Cash flows from operating activities:
Net cash provided by operating activities	13,044	90,349
Cash flows from investing activities:
Contributions to unconsolidated joint ventures	0	0
Return of investments in unconsolidated joint ventures	0	0
Proceeds from sale of building		0
Purchases of property and equipment, net	(3,662)	(9,231)
Intercompany	0	0
Net cash used in investing activities	(3,662)	(9,231)
Cash flows from financing activities:
Repayment of senior notes		0
Borrowings under revolving credit facility		0
Repayments under revolving credit facility		0
Payments on mortgages and land contracts due to land sellers and other loans	0	0
Issuance of common stock under employee stock plans	0	0
Payments of cash dividends	0	0
Tax payments associated with stock-based compensation awards	0	0
Intercompany	(10,968)	(98,444)
Net cash used in financing activities	(10,968)	(98,444)
Net increase (decrease) in cash and cash equivalents	(1,586)	(17,326)
Cash and cash equivalents at beginning of period	31,458	30,873
Cash and cash equivalents at end of period	29,872	13,547
Consolidating Adjustments [Member]
Cash flows from operating activities:
Net cash provided by operating activities	0	0
Cash flows from investing activities:
Contributions to unconsolidated joint ventures	0	0
Return of investments in unconsolidated joint ventures	0	0
Proceeds from sale of building		0
Purchases of property and equipment, net	0	0
Intercompany	(256,600)	274,010
Net cash used in investing activities	(256,600)	274,010
Cash flows from financing activities:
Proceeds from issuance of debt		0
Issuance costs for unsecured revolving credit facility		0
Repayment of senior notes		0
Borrowings under revolving credit facility		0
Repayments under revolving credit facility		0
Payments on mortgages and land contracts due to land sellers and other loans	0	0
Issuance of common stock under employee stock plans	0	0
Payments of cash dividends	0	0
Tax payments associated with stock-based compensation awards	0	0
Intercompany	256,600	(274,010)
Net cash used in financing activities	256,600	(274,010)
Net increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents at beginning of period	0	0
Cash and cash equivalents at end of period	$ 0	$ 0