Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Nov. 30, 2017
Segment Reporting Information [Line Items]
Operations	Operations. KB Home is a builder of attached and detached single-family residential homes, townhomes and condominiums. As of November 30, 2017, we conducted ongoing operations in Arizona, California, Colorado, Florida, Nevada, North Carolina and Texas. We also offer various insurance products to our homebuyers in the same markets where we build homes, and provide title services in the majority of our markets located within our Central and Southeast homebuilding reporting segments. Until October 2016, we provided mortgage banking services, including mortgage loan originations, to our homebuyers indirectly through HCM, a joint venture of a subsidiary of ours and a subsidiary of Nationstar. Since June 2017, we have been providing mortgage banking services, including mortgage loan originations, to our homebuyers indirectly through KBHS, an unconsolidated joint venture we formed with Stearns in the 2016 fourth quarter.
Basis of Presentation	Basis of Presentation. Our consolidated financial statements have been prepared in accordance with GAAP and include our accounts and those of the consolidated subsidiaries in which we have a controlling financial interest. All intercompany balances and transactions have been eliminated in consolidation. Investments in unconsolidated joint ventures in which we have less than a controlling financial interest are accounted for using the equity method.
Use of Estimates	Use of Estimates. The preparation of financial statements in conformity with GAAP requires management to make estimates and judgments that affect the amounts reported in the consolidated financial statements and accompanying notes. Actual results could differ from those estimates.
Cash and Cash Equivalents and Restricted Cash	Cash and Cash Equivalents. We consider all highly liquid short-term investments purchased with an original maturity of three months or less to be cash equivalents.
Property and Equipment and Depreciation	Property and Equipment and Depreciation. Property and equipment are recorded at cost and are depreciated over their estimated useful lives, which generally range from two to 10 years, using the straight-line method. Repair and maintenance costs are expensed as incurred.
Homebuilding Operations	Homebuilding Operations. Revenues from housing and other real estate sales are recognized when sales are closed and title passes to the homebuyer. Sales are closed when all of the following conditions are met: a sale is consummated, a sufficient down payment is received, the earnings process is complete and the collection of any remaining receivables is reasonably assured. Concurrent with the recognition of revenues in our consolidated statements of operations, sales incentives in the form of price concessions on the selling price of a home are recorded as a reduction of revenues, while the costs of sales incentives in the form of free or discounted products or services to homebuyers, including option upgrades and closing cost allowances used to cover a portion of the fees and costs charged to a homebuyer, are reflected as construction and land costs. Construction and land costs are comprised of direct and allocated costs, including estimated future costs for the limited warranty we provide on our homes, and certain amenities within a community. Land acquisition, land development and other common costs are generally allocated on a relative fair value basis to the homes or lots within the applicable community or land parcel. Land acquisition and land development costs include related interest and real estate taxes. Housing and land inventories are stated at cost, unless the carrying value is determined not to be recoverable, in which case the affected inventories are written down to fair value or fair value less associated costs to sell. Real estate assets, such as our housing and land inventories, are tested for recoverability whenever events or changes in circumstances indicate that their carrying value may not be recoverable. Recoverability is measured by comparing the carrying value of an asset to the undiscounted future net cash flows expected to be generated by the asset. These impairment evaluations are significantly impacted by estimates for the amounts and timing of future revenues, costs and expenses, and other factors. If the carrying value of a real estate asset is determined not to be recoverable, the impairment charge to be recognized is measured by the amount by which the carrying value of the affected asset exceeds its estimated fair value. For land held for sale, if the fair value less associated costs to sell exceeds the asset’s carrying value, no impairment charge is recognized.
Capitalized Interest	Capitalized Interest. Interest is capitalized to inventories while the related communities or land parcels are being actively developed and until homes are completed or the land is available for immediate sale. Capitalized interest is amortized to construction and land costs as the related inventories are delivered to homebuyers or land buyers (as applicable). For land held for future development or sale, applicable interest is expensed as incurred.
Fair Value Measurements	Fair Value Measurements. Fair value measurements are used for inventories on a nonrecurring basis when events and circumstances indicate that their carrying value is not recoverable. For these real estate assets, fair value is determined based on the estimated future net cash flows discounted for inherent risk associated with each such asset, or other valuation techniques. Our financial instruments consist of cash and cash equivalents, senior notes, convertible senior notes, and mortgages and land contracts due to land sellers and other loans. Fair value measurements of financial instruments are determined by various market data and other valuation techniques as appropriate. When available, we use quoted market prices in active markets to determine fair value.
Warranty Costs	Warranty Costs. We provide a limited warranty on all of our homes. We estimate the costs that may be incurred under each limited warranty and record a liability in the amount of such costs at the time the revenue associated with the sale of each home is recognized. Our primary assumption in estimating the amounts we accrue for warranty costs is that historical claims experience is a strong indicator of future claims experience. Factors that affect our warranty liability include the number of homes delivered, historical and anticipated rates of warranty claims, and cost per claim. We periodically assess the adequacy of our accrued warranty liability and adjust the amount as necessary based on our assessment. Our warranty liability is presented on a gross basis for all years without consideration of recoveries and amounts we have paid on behalf of and expect to recover from other parties, if any. Estimates of recoveries and amounts we have paid on behalf of and expect to recover from other parties, if any, are recorded as receivables when such recoveries are considered probable.
Self-Insurance	Self-Insurance. We self-insure a portion of our overall risk through the use of a captive insurance subsidiary. We also maintain certain other insurance policies. We record liabilities based on the estimated costs required to cover reported claims, claims incurred but not yet reported, and claim adjustment expenses. These estimated costs are based on an actuarial analysis of our historical claims and expense data, as well as industry data. Our self-insurance liability is presented on a gross basis for all years without consideration of insurance recoveries and amounts we have paid on behalf of and expect to recover from other parties, if any. Estimates of insurance recoveries and amounts we have paid on behalf of and expect to recover from other parties, if any, are recorded as receivables when such recoveries are considered probable.
Advertising Costs	Advertising Costs. We expense advertising costs as incurred.
Legal Fees	Legal Fees. Legal fees associated with litigation and similar proceedings that are not expected to provide a benefit in future periods are generally expensed as incurred. Legal fees associated with land acquisition and development and other activities that are expected to provide a benefit in future periods are capitalized to inventories in our consolidated balance sheets as incurred.
Stock-Based Compensation	Stock-Based Compensation. We measure and recognize compensation expense associated with our grant of equity-based awards at an amount equal to the fair value of share-based payments granted under compensation arrangements over the vesting period. We estimate the fair value of stock options and Director Plan SARs granted using the Black-Scholes option-pricing model with assumptions based primarily on historical data. We report the tax benefit resulting from tax deductions in excess of the compensation expense recognized for stock options in our consolidated statements of cash flows as an operating cash outflow and a financing cash inflow.
Income Taxes	Income Taxes. The provision for, or benefit from, income taxes is calculated using the asset and liability method, under which deferred tax assets and liabilities are recorded based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Deferred tax assets are evaluated on a quarterly basis to determine if adjustments to the valuation allowance are required. This evaluation is based on the consideration of all available positive and negative evidence using a “more likely than not” standard with respect to whether deferred tax assets will be realized. The ultimate realization of our deferred tax assets depends primarily on our ability to generate future taxable income during the periods in which the related temporary differences in the financial basis and the tax basis of the assets become deductible. The value of our deferred tax assets in our consolidated balance sheets depends on applicable income tax rates.
Accumulated Other Comprehensive Loss	Accumulated Other Comprehensive Loss. The accumulated balances of other comprehensive loss in the consolidated balance sheets as of November 30, 2017 and 2016 were comprised solely of adjustments recorded directly to accumulated other comprehensive loss related to our benefit plan obligations. Such adjustments are made annually as of November 30, when our benefit plan obligations are remeasured.
Earnings Per Share	Earnings Per Share. We compute earnings per share using the two-class method, which is an allocation of earnings between the holders of common stock and a company’s participating security holders. Our outstanding nonvested shares of restricted stock contain non-forfeitable rights to dividends and, therefore, are considered participating securities for purposes of computing earnings per share pursuant to the two-class method. We had no other participating securities at November 30, 2017, 2016 or 2015.
Recent Accounting Pronouncements Not Yet Adopted	Recent Accounting Pronouncements Not Yet Adopted. In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update No. 2014-09, “Revenue from Contracts with Customers (Topic 606)” (“ASU 2014-09”). The core principle of ASU 2014-09 is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In August 2015, the FASB issued Accounting Standards Update No. 2015-14, “Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date,” which delayed the effective date of ASU 2014-09 by one year. In 2016 and 2017, the FASB issued accounting standards updates that amended several aspects of ASU 2014-09. ASU 2014-09, as amended, is effective for us beginning December 1, 2018 (with early adoption permitted beginning in our 2018 fiscal year) and allows for full retrospective or modified retrospective methods of adoption. We expect to adopt ASU 2014-09 under the modified retrospective method in our 2019 first quarter. We are currently evaluating the potential impact of adopting this guidance on our consolidated financial statements and disclosures, and have been involved in industry-specific discussions with the FASB on the treatment of certain items. We do not believe the adoption of ASU 2014-09 will have a material impact on the amount or timing of our homebuilding revenues. We are also continuing to evaluate the impact adopting this guidance may have on other aspects of our business. In February 2016, the FASB issued Accounting Standards Update No. 2016-02, “Leases (Topic 842)” (“ASU 2016-02”). ASU 2016-02 will require lessees to recognize on the balance sheet the assets and liabilities for the rights and obligations created by those leases. Under ASU 2016-02, a lessee will be required to recognize assets and liabilities for leases with terms of more than 12 months. Lessor accounting remains substantially similar to current GAAP. In addition, disclosures of leasing activities are to be expanded to include qualitative along with specific quantitative information. ASU 2016-02 will be effective for us beginning December 1, 2019 (with early adoption permitted). ASU 2016-02 mandates a modified retrospective transition method. We are currently evaluating the potential impact of adopting this guidance on our consolidated financial statements. In March 2016, the FASB issued Accounting Standards Update No. 2016-09, “Compensation — Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting” (“ASU 2016-09”), which simplifies several aspects of the accounting for share-based payment transactions. ASU 2016-09 requires excess tax benefits and deficiencies from share-based payment awards to be recorded in income tax expense in the consolidated statement of operations. Currently, excess tax benefits and deficiencies are recognized in paid-in capital in the consolidated balance sheet. This change is required to be applied prospectively. In addition, ASU 2016-09 changes the accounting for statutory tax withholding requirements, classification in the statement of cash flows and provides an option to continue to estimate forfeitures or account for forfeitures as they occur. We will adopt ASU 2016-09 effective December 1, 2017 and will elect to continue to estimate forfeitures. We expect ASU 2016-09 to result in increased volatility to our income tax expense in our consolidated statements of operations in 2018 and future periods, the magnitude of which will depend on, among other things, the price of our common stock and the timing and volume of share-based payment award activity, such as employee exercises of stock options and vesting of restricted stock awards and PSUs. In August 2016, the FASB issued Accounting Standards Update No. 2016-15, “Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments” (“ASU 2016-15”). ASU 2016-15 provides guidance on how certain cash receipts and cash payments are to be presented and classified in the statement of cash flows. ASU 2016-15 will be effective for us beginning December 1, 2018 (with early adoption permitted). We do not expect the adoption of ASU 2016-15 to have a material impact on our consolidated financial statements. In November 2016, the FASB issued Accounting Standards Update No. 2016-18, “Statement of Cash Flows (Topic 230): Restricted Cash” (“ASU 2016-18”). ASU 2016-18 requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. Therefore, amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. ASU 2016-18 will be effective for us beginning December 1, 2018 (with early adoption permitted) and will be applied using a retrospective transition method to each period presented. We do not expect the adoption of ASU 2016-18 to have a material impact on our consolidated financial statements.
Adoption of New Accounting Pronouncement	Recent Accounting Pronouncements Not Yet Adopted. In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update No. 2014-09, “Revenue from Contracts with Customers (Topic 606)” (“ASU 2014-09”). The core principle of ASU 2014-09 is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In August 2015, the FASB issued Accounting Standards Update No. 2015-14, “Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date,” which delayed the effective date of ASU 2014-09 by one year. In 2016 and 2017, the FASB issued accounting standards updates that amended several aspects of ASU 2014-09. ASU 2014-09, as amended, is effective for us beginning December 1, 2018 (with early adoption permitted beginning in our 2018 fiscal year) and allows for full retrospective or modified retrospective methods of adoption. We expect to adopt ASU 2014-09 under the modified retrospective method in our 2019 first quarter. We are currently evaluating the potential impact of adopting this guidance on our consolidated financial statements and disclosures, and have been involved in industry-specific discussions with the FASB on the treatment of certain items. We do not believe the adoption of ASU 2014-09 will have a material impact on the amount or timing of our homebuilding revenues. We are also continuing to evaluate the impact adopting this guidance may have on other aspects of our business. In February 2016, the FASB issued Accounting Standards Update No. 2016-02, “Leases (Topic 842)” (“ASU 2016-02”). ASU 2016-02 will require lessees to recognize on the balance sheet the assets and liabilities for the rights and obligations created by those leases. Under ASU 2016-02, a lessee will be required to recognize assets and liabilities for leases with terms of more than 12 months. Lessor accounting remains substantially similar to current GAAP. In addition, disclosures of leasing activities are to be expanded to include qualitative along with specific quantitative information. ASU 2016-02 will be effective for us beginning December 1, 2019 (with early adoption permitted). ASU 2016-02 mandates a modified retrospective transition method. We are currently evaluating the potential impact of adopting this guidance on our consolidated financial statements. In March 2016, the FASB issued Accounting Standards Update No. 2016-09, “Compensation — Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting” (“ASU 2016-09”), which simplifies several aspects of the accounting for share-based payment transactions. ASU 2016-09 requires excess tax benefits and deficiencies from share-based payment awards to be recorded in income tax expense in the consolidated statement of operations. Currently, excess tax benefits and deficiencies are recognized in paid-in capital in the consolidated balance sheet. This change is required to be applied prospectively. In addition, ASU 2016-09 changes the accounting for statutory tax withholding requirements, classification in the statement of cash flows and provides an option to continue to estimate forfeitures or account for forfeitures as they occur. We will adopt ASU 2016-09 effective December 1, 2017 and will elect to continue to estimate forfeitures. We expect ASU 2016-09 to result in increased volatility to our income tax expense in our consolidated statements of operations in 2018 and future periods, the magnitude of which will depend on, among other things, the price of our common stock and the timing and volume of share-based payment award activity, such as employee exercises of stock options and vesting of restricted stock awards and PSUs. In August 2016, the FASB issued Accounting Standards Update No. 2016-15, “Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments” (“ASU 2016-15”). ASU 2016-15 provides guidance on how certain cash receipts and cash payments are to be presented and classified in the statement of cash flows. ASU 2016-15 will be effective for us beginning December 1, 2018 (with early adoption permitted). We do not expect the adoption of ASU 2016-15 to have a material impact on our consolidated financial statements. In November 2016, the FASB issued Accounting Standards Update No. 2016-18, “Statement of Cash Flows (Topic 230): Restricted Cash” (“ASU 2016-18”). ASU 2016-18 requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. Therefore, amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. ASU 2016-18 will be effective for us beginning December 1, 2018 (with early adoption permitted) and will be applied using a retrospective transition method to each period presented. We do not expect the adoption of ASU 2016-18 to have a material impact on our consolidated financial statements.
Segment Reporting	four homebuilding reporting segments based primarily on similarities in economic and geographic characteristics, product types, regulatory environments, methods used to sell and construct homes and land acquisition characteristics. We also have one financial services reporting segment. Management evaluates segment performance primarily based on segment pretax results. As of November 30, 2017, our homebuilding reporting segments conducted ongoing operations in the following states: West Coast: California Southwest: Arizona and Nevada Central: Colorado and Texas Southeast: Florida and North Carolina Our homebuilding reporting segments are engaged in the acquisition and development of land primarily for residential purposes and offer a wide variety of homes that are designed to appeal to first-time, first move-up and active adult homebuyers. Our homebuilding operations generate most of their revenues from the delivery of completed homes to homebuyers. They also earn revenues from the sale of land. In 2016, we announced that we had begun a transition out of the Metro Washington, D.C. market that was substantially completed in 2017. Our operations in the Metro Washington, D.C. market consisted of communities in Maryland and Virginia, which were included in our Southeast homebuilding reporting segment, and represented 2% of our consolidated homebuilding revenues for the year ended November 30, 2016. As described in Note 7 – Inventory Impairments and Land Option Contract Abandonments, we recorded inventory impairment and land option contract abandonment charges related to this transition during the year ended November 30, 2016. Our financial services reporting segment offers property and casualty insurance and, in certain instances, earthquake, flood and personal property insurance to our homebuyers in the same markets as our homebuilding reporting segments, and provides title services in the majority of our markets located within our Central and Southeast homebuilding reporting segments. This segment earns revenues primarily from insurance commissions and from the provision of title services. Until October 2016, we provided mortgage banking services, including mortgage loan originations, to our homebuyers indirectly through HCM, a joint venture of a subsidiary of ours and a subsidiary of Nationstar. Through these respective subsidiaries, we have a 49.9% ownership interest and Nationstar has a 50.1% ownership interest in HCM, with Nationstar providing management oversight of HCM’s operations. In the 2016 fourth quarter, we and Nationstar began the process to wind down HCM and transfer HCM’s operations and certain assets to Stearns. In 2016, a subsidiary of ours and a subsidiary of Stearns formed KBHS, an unconsolidated mortgage banking joint venture, to offer mortgage banking services, including mortgage loan originations, to our homebuyers. We and Stearns each have a 50.0% ownership interest, with Stearns providing management oversight of KBHS’ operations. KBHS was operational in all of our served markets as of June 2017. KBHS did not have an impact on our consolidated statement of operations for the year ended November 30, 2016. Our homebuyers may select any lender of their choice to obtain mortgage financing for the purchase of their home. The financial services reporting segment is separately reported in our consolidated financial statements. Corporate and other is a non-operating segment that develops and oversees the implementation of company-wide strategic initiatives and provides support to our reporting segments by centralizing certain administrative functions. Corporate management is responsible for, among other things, evaluating and selecting the geographic markets in which we operate, consistent with our overall business strategy; allocating capital resources to markets for land acquisition and development activities; making major personnel decisions related to employee compensation and benefits; and monitoring the financial and operational performance of our divisions. Corporate and other includes general and administrative expenses related to operating our corporate headquarters. A portion of the expenses incurred by Corporate and other is allocated to our homebuilding reporting segments. Our reporting segments follow the same accounting policies used for our consolidated financial statements as described in Note 1 – Summary of Significant Accounting Policies. The results of each reporting segment are not necessarily indicative of the results that would have occurred had the segment been an independent, stand-alone entity during the periods presented, nor are they indicative of the results to be expected in future periods.
Inventory Impairment	Each community or land parcel in our owned inventory is assessed to determine if indicators of potential impairment exist. Impairment indicators are assessed separately for each community or land parcel on a quarterly basis and include, but are not limited to, the following: significant decreases in net orders, average selling prices, volume of homes delivered, gross profit margins on homes delivered or projected gross profit margins on homes in backlog or future deliveries; significant increases in budgeted land development and home construction costs or cancellation rates; or projected losses on expected future land sales. If indicators of potential impairment exist for a community or land parcel, the identified asset is evaluated for recoverability.
Land under Option Arrangements	Our inventory controlled under land option contracts and other similar contracts is assessed to determine whether it continues to meet our investment return standards. Assessments are made separately for each optioned land parcel on a quarterly basis and are affected by the following factors relative to the market in which the asset is located, among others: current and/or anticipated net orders, average selling prices and volume of homes delivered; estimated land development and home construction costs; and projected profitability on expected future housing or land sales. When a decision is made not to exercise certain land option contracts and other similar contracts due to market conditions and/or changes in our marketing strategy, we write off the related inventory costs, including non-refundable deposits and unrecoverable pre-acquisition costs.
Financial services [Member]
Segment Reporting Information [Line Items]
Operations	Financial Services Operations. Our financial services reporting segment generates revenues primarily from insurance commissions and title services. Revenues from insurance commissions and title services are recognized when policies are issued, which generally occurs at the time each applicable home is closed.