Supplemental Guarantor Information (Condensed Consolidated Statements of Cash Flows) (Details) - USD ($) $ in Thousands	6 Months Ended
	May 31, 2020	May 31, 2019
Cash flows from operating activities:
Net cash provided by (used in) operating activities	$ 154,694	$ (180,334)
Cash flows from investing activities:
Contributions to unconsolidated joint ventures	(3,586)	(4,245)
Return of investments in unconsolidated joint ventures	500	5,001
Proceeds from sale of building	0	5,804
Purchases of property and equipment, net	(15,224)	(22,264)
Intercompany	0	0
Net cash used in investing activities	(18,310)	(15,704)
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	330,000
Repayments under revolving credit facility	0	(280,000)
Payments on mortgages and land contracts due to land sellers and other loans	(1,063)	(28,020)
Issuance of common stock under employee stock plans	8,404	16,462
Payments of cash dividends	(16,331)	(4,455)
Tax payments associated with stock-based compensation awards	(6,219)	(3,345)
Intercompany	0	0
Net cash used in financing activities	(15,209)	(199,317)
Net increase (decrease) in cash and cash equivalents	121,175	(395,355)
Cash and cash equivalents at beginning of period	454,858	575,119
Cash and cash equivalents at end of period	576,033	179,764
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 (used in) operating activities	(14,150)	35,547
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	(3,111)	(3,241)
Intercompany	153,647	(196,595)
Net cash used in investing activities	150,536	(199,836)
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		330,000
Repayments under revolving credit facility		(280,000)
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	16,462
Payments of cash dividends	(16,331)	(4,455)
Tax payments associated with stock-based compensation awards	(6,219)	(3,345)
Intercompany	0	0
Net cash used in financing activities	(14,146)	(171,297)
Net increase (decrease) in cash and cash equivalents	122,240	(335,586)
Cash and cash equivalents at beginning of period	357,966	429,977
Cash and cash equivalents at end of period	480,206	94,391
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Cash flows from operating activities:
Net cash provided by (used in) operating activities	166,394	(308,291)
Cash flows from investing activities:
Contributions to unconsolidated joint ventures	(3,586)	(4,245)
Return of investments in unconsolidated joint ventures	500	5,001
Proceeds from sale of building		5,804
Purchases of property and equipment, net	(9,714)	(11,360)
Intercompany	0	0
Net cash used in investing activities	(12,800)	(4,800)
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	(1,063)	(28,020)
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	(152,555)	298,278
Net cash used in financing activities	(153,618)	270,258
Net increase (decrease) in cash and cash equivalents	(24)	(42,833)
Cash and cash equivalents at beginning of period	65,434	114,269
Cash and cash equivalents at end of period	65,410	71,436
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Cash flows from operating activities:
Net cash provided by (used in) operating activities	2,450	92,410
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	(2,399)	(7,663)
Intercompany	0	0
Net cash used in investing activities	(2,399)	(7,663)
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	(1,092)	(101,683)
Net cash used in financing activities	(1,092)	(101,683)
Net increase (decrease) in cash and cash equivalents	(1,041)	(16,936)
Cash and cash equivalents at beginning of period	31,458	30,873
Cash and cash equivalents at end of period	30,417	13,937
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	(153,647)	196,595
Net cash used in investing activities	(153,647)	196,595
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	153,647	(196,595)
Net cash used in financing activities	153,647	(196,595)
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