Supplemental Guarantor Information (Condensed Consolidated Statements of Cash Flows) (Details) - USD ($) $ in Thousands	9 Months Ended
	Aug. 31, 2018	Aug. 31, 2017
Cash flows from operating activities:
Net cash used in operating activities	$ (49,508)	$ 103,270
Cash flows from investing activities:
Contributions to unconsolidated joint ventures	(15,640)	(15,154)
Return of investments in unconsolidated joint ventures	9,934	8,159
Purchases of property and equipment, net	(4,137)	(6,643)
Intercompany	0	0
Net cash used in investing activities	(9,843)	(13,638)
Cash flows from financing activities:
Repayment of senior notes	(300,000)	(105,326)
Issuance costs for unsecured revolving credit facility	0	(1,711)
Borrowings under revolving credit facility	70,000	0
Repayments under revolving credit facility	(70,000)	0
Payments on mortgages and land contracts due to land sellers and other loans	(10,494)	(92,443)
Issuance of common stock under employee stock plans	17,433	20,677
Payments of cash dividends	(6,686)	(6,479)
Tax payments associated with stock-based compensation awards	(6,787)	(2,543)
Intercompany	0	0
Net cash used in financing activities	(306,534)	(187,825)
Net decrease in cash and cash equivalents	(365,885)	(98,193)
Cash and cash equivalents at beginning of period	720,861	593,000
Cash and cash equivalents at end of period	354,976	494,807
KB Home Corporate
Cash flows from operating activities:
Net cash used in operating activities	50,507	82,480
Cash flows from investing activities:
Contributions to unconsolidated joint ventures	0	0
Return of investments in unconsolidated joint ventures	0	0
Purchases of property and equipment, net	(3,508)	(5,875)
Intercompany	(80,955)	(43,367)
Net cash used in investing activities	(84,463)	(49,242)
Cash flows from financing activities:
Repayment of senior notes	(300,000)	(105,326)
Issuance costs for unsecured revolving credit facility		(1,711)
Borrowings under revolving credit facility	70,000
Repayments under revolving credit facility	(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	17,433	20,677
Payments of cash dividends	(6,686)	(6,479)
Tax payments associated with stock-based compensation awards	(6,787)	(2,543)
Intercompany	0	0
Net cash used in financing activities	(296,040)	(95,382)
Net decrease in cash and cash equivalents	(329,996)	(62,144)
Cash and cash equivalents at beginning of period	575,193	463,100
Cash and cash equivalents at end of period	245,197	400,956
Guarantor Subsidiaries
Cash flows from operating activities:
Net cash used in operating activities	(38,248)	30,480
Cash flows from investing activities:
Contributions to unconsolidated joint ventures	(15,640)	(9,899)
Return of investments in unconsolidated joint ventures	9,934	3,169
Purchases of property and equipment, net	(457)	(719)
Intercompany	0	0
Net cash used in investing activities	(6,163)	(7,449)
Cash flows from financing activities:
Repayment of senior notes	0	0
Issuance costs for unsecured revolving credit facility		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	(9,574)	(92,443)
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	37,525	51,595
Net cash used in financing activities	27,951	(40,848)
Net decrease in cash and cash equivalents	(16,460)	(17,817)
Cash and cash equivalents at beginning of period	102,661	100,439
Cash and cash equivalents at end of period	86,201	82,622
Non-Guarantor Subsidiaries
Cash flows from operating activities:
Net cash used in operating activities	(61,767)	(9,690)
Cash flows from investing activities:
Contributions to unconsolidated joint ventures	0	(5,255)
Return of investments in unconsolidated joint ventures	0	4,990
Purchases of property and equipment, net	(172)	(49)
Intercompany	0	0
Net cash used in investing activities	(172)	(314)
Cash flows from financing activities:
Repayment of senior notes	0	0
Issuance costs for unsecured revolving credit facility		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	(920)	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	43,430	(8,228)
Net cash used in financing activities	42,510	(8,228)
Net decrease in cash and cash equivalents	(19,429)	(18,232)
Cash and cash equivalents at beginning of period	43,007	29,461
Cash and cash equivalents at end of period	23,578	11,229
Consolidating Adjustments
Cash flows from operating activities:
Net cash 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
Purchases of property and equipment, net	0	0
Intercompany	80,955	43,367
Net cash used in investing activities	80,955	43,367
Cash flows from financing activities:
Repayment of senior notes	0	0
Issuance costs for unsecured revolving credit facility		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	(80,955)	(43,367)
Net cash used in financing activities	(80,955)	(43,367)
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