Supplemental Guarantor Information (Condensed Consolidated Statements of Cash Flows) (Details) - USD ($) $ in Thousands		9 Months Ended
	Feb. 20, 2019	Aug. 31, 2019	Aug. 31, 2018
Cash flows from operating activities:
Net cash provided by (used in) operating activities		$ (152,144)	$ (49,508)
Cash flows from investing activities:
Contributions to unconsolidated joint ventures		(7,656)	(15,640)
Return of investments in unconsolidated joint ventures		5,001	9,934
Proceeds from sale of building		5,800	0
Purchases of property and equipment, net		(32,211)	(4,137)
Intercompany		0	0
Net cash used in investing activities		(29,062)	(9,843)
Cash flows from financing activities:
Proceeds from issuance of debt	$ 400,000	405,250	0
Issuance costs for unsecured revolving credit facility		(5,209)	0
Repayment of senior notes		(630,000)	(300,000)
Borrowings under revolving credit facility		460,000	70,000
Repayments under revolving credit facility		(410,000)	(70,000)
Payments on mortgages and land contracts due to land sellers and other loans		(32,149)	(10,494)
Issuance of common stock under employee stock plans		18,729	17,433
Payments of cash dividends		(12,352)	(6,686)
Tax payments associated with stock-based compensation awards		(3,345)	(6,787)
Intercompany		0	0
Net cash used in financing activities		(209,076)	(306,534)
Net decrease in cash and cash equivalents		(390,282)	(365,885)
Cash and cash equivalents at beginning of period		575,119	720,861
Cash and cash equivalents at end of period		184,837	354,976
Reportable Legal Entities [Member] | KB Home Corporate [Member]
Cash flows from operating activities:
Net cash provided by (used in) operating activities		92,935	50,507
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		(4,728)	(3,508)
Intercompany		(274,010)	(80,955)
Net cash used in investing activities		(278,738)	(84,463)
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)	(300,000)
Borrowings under revolving credit facility		460,000	70,000
Repayments under revolving credit facility		(410,000)	(70,000)
Payments on mortgages and land contracts due to land sellers and other loans		0	0
Issuance of common stock under employee stock plans		18,729	17,433
Payments of cash dividends		(12,352)	(6,686)
Tax payments associated with stock-based compensation awards		(3,345)	(6,787)
Intercompany		0	0
Net cash used in financing activities		(176,927)	(296,040)
Net decrease in cash and cash equivalents		(362,730)	(329,996)
Cash and cash equivalents at beginning of period		429,977	575,193
Cash and cash equivalents at end of period		67,247	245,197
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Cash flows from operating activities:
Net cash provided by (used in) operating activities		(335,428)	(78,593)
Cash flows from investing activities:
Contributions to unconsolidated joint ventures		(7,656)	(15,640)
Return of investments in unconsolidated joint ventures		5,001	9,934
Proceeds from sale of building		5,804
Purchases of property and equipment, net		(18,252)	(520)
Intercompany		0	0
Net cash used in investing activities		(15,103)	(6,226)
Cash flows from financing activities:
Proceeds from issuance of debt		0
Issuance costs for unsecured revolving credit facility		0
Repayment of senior notes		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		(32,149)	(9,574)
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		372,454	83,560
Net cash used in financing activities		340,305	73,986
Net decrease in cash and cash equivalents		(10,226)	(10,833)
Cash and cash equivalents at beginning of period		114,269	104,120
Cash and cash equivalents at end of period		104,043	93,287
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Cash flows from operating activities:
Net cash provided by (used in) operating activities		90,349	(21,422)
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		(9,231)	(109)
Intercompany		0	0
Net cash used in investing activities		(9,231)	(109)
Cash flows from financing activities:
Proceeds from issuance of debt		0
Issuance costs for unsecured revolving credit facility		0
Repayment of senior notes		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)
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		(98,444)	(2,605)
Net cash used in financing activities		(98,444)	(3,525)
Net decrease in cash and cash equivalents		(17,326)	(25,056)
Cash and cash equivalents at beginning of period		30,873	41,548
Cash and cash equivalents at end of period		13,547	16,492
Consolidating Adjustments [Member]
Cash flows from operating activities:
Net cash provided by (used in) 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		274,010	80,955
Net cash used in investing activities		274,010	80,955
Cash flows from financing activities:
Proceeds from issuance of debt		0
Issuance costs for unsecured revolving credit facility		0
Repayment of senior notes		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
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		(274,010)	(80,955)
Net cash used in financing activities		(274,010)	(80,955)
Net 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