Basis of Presentation and Significant Accounting Policies (Policies)	9 Months Ended
Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The Company is an exempted Bermuda limited liability company whose principal businesses are conducted through its subsidiaries and other affiliates. The Company’s headquarters is located at 26 Reid Street, Hamilton, Bermuda HM 11, its principal executive office is located at 23 South Main Street, Suite 3B, Hanover, New Hampshire 03755-2053 and its registered office is located at Clarendon House, 2 Church Street, Hamilton, Bermuda HM 11. The Company’s website is located at www.whitemountains.com. The information contained on White Mountains’s website is not incorporated by reference into, and is not a part of, this report. The accompanying consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) and include the accounts of White Mountains Insurance Group, Ltd. (the “Company” or the “Registrant”), its subsidiaries (collectively with the Company, “White Mountains”) and other entities required to be consolidated under GAAP.
Consolidation Principles	Consolidation Principles Under GAAP, the Company is required to consolidate any entity in which it holds a controlling financial interest. A controlling financial interest is usually in the form of an investment representing the majority of the subsidiary’s voting interests. However, a controlling financial interest may also arise from a financial interest in a variable interest entity (“VIE”) through arrangements that do not involve ownership of voting interests. The Company consolidates a VIE if it determines that it is the primary beneficiary. The primary beneficiary is defined as the entity who holds a variable interest that gives it both the power to direct the VIE’s activities that most significantly impact its economic performance and the obligation to absorb losses of, or the right to receive returns from, the VIE that could potentially be significant to the VIE. Intercompany transactions have been eliminated in consolidation. These interim financial statements include all adjustments considered necessary by management to fairly state the financial position, results of operations and cash flows of White Mountains. These interim financial statements may not be indicative of financial results for the full year and should be read in conjunction with the Company’s 2020 Annual Report on Form 10-K.
Business Combinations	Business Combinations White Mountains accounts for purchases of businesses using the acquisition method, which requires the measurement of assets acquired, including goodwill and other intangible assets, and liabilities assumed, including contingent liabilities, at their estimated fair values as of the acquisition date. The acquisition date fair values represent management’s best estimates and are based upon established valuation techniques, reasonable assumptions and, where appropriate, valuations performed by independent third parties. In circumstances where additional information is required in order to determine the acquisition date fair value of balance sheet amounts, provisional amounts may be recorded as of the acquisition date and may be subject to subsequent adjustment throughout the measurement period, which is up to one year from the acquisition date. Measurement period adjustments are recognized in the period in which they are determined. The results of operations and cash flows of businesses acquired are included in the consolidated financial statements from the date of acquisition. White Mountains accounts for purchases of other intangible assets that do not meet the definition of a business as asset acquisitions. Asset acquisitions are recognized at the amount of consideration paid, which is deemed to equal fair value.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Fair Value Measurements	Fair Value Measurements Fair value measurements are categorized into a hierarchy that distinguishes between inputs based on market data from independent sources (observable inputs) and a reporting entity’s internal assumptions based upon the best information available when external market data is limited or unavailable (unobservable inputs). Quoted prices in active markets for identical assets or liabilities have the highest priority (“Level 1”), followed by observable inputs other than quoted prices, including prices for similar but not identical assets or liabilities (“Level 2”) and unobservable inputs, including the reporting entity’s estimates of the assumptions that market participants would use, having the lowest priority (“Level 3”).
Reportable Segments	Reportable Segments White Mountains has determined its reportable segments based on the nature of the underlying businesses, the manner in which the Company’s subsidiaries and affiliates are organized and managed and the organization of the financial information provided to the chief operating decision maker to assess performance and make decisions regarding allocation of resources. As of September 30, 2021, White Mountains’s reportable segments were HG Global/BAM, Ark, NSM, Kudu and Other Operations. The HG Global/BAM segment consists of HG Global Ltd. and its wholly-owned subsidiaries (“HG Global”) and the consolidated results of Build America Mutual Assurance Company (“BAM”) (collectively, “HG Global/BAM”). BAM is the first and only mutual municipal bond insurance company in the United States. By insuring the timely payment of principal and interest, BAM provides market access to, and lowers interest expense for, issuers of municipal bonds used to finance essential public purposes such as schools, utilities and transportation facilities. BAM is owned by and operated for the benefit of its members, the municipalities that purchase BAM’s insurance for their debt issuances. HG Global was established to fund the startup of BAM and, through its wholly-owned subsidiary, HG Re Ltd. (“HG Re”), to provide up to 15%-of-par, first loss reinsurance protection for policies underwritten by BAM. For capital appreciation bonds, par is adjusted to the estimated equivalent par value for current interest paying bonds. HG Global, together with its subsidiaries, funded the initial capitalization of BAM through the purchase of $503.0 million of surplus notes issued by BAM, consisting of $203.0 million of Series A Notes and $300.0 million of Series B Notes (the “BAM Surplus Notes”). As of September 30, 2021 and December 31, 2020, White Mountains owned 96.9% of HG Global’s preferred equity and 88.4% of its common equity. White Mountains does not have an ownership interest in BAM. However, White Mountains is required to consolidate BAM’s results in its financial statements because BAM is a VIE for which White Mountains is the primary beneficiary. BAM’s results are all attributed to non-controlling interests. The Ark segment consists of Ark Insurance Holdings Limited and its subsidiaries (collectively, “Ark”). Ark writes a diversified portfolio of reinsurance and insurance, including property, marine & energy, specialty, accident & health and casualty, through Lloyd’s of London (“Lloyd’s”) Syndicates 4020 and 3902 (the “Syndicates”). Beginning in January 2021, Ark began writing certain classes of its business through Group Ark Insurance Limited (“GAIL”), Ark’s wholly-owned Class 4 Bermuda-based insurance and reinsurance company. As of September 30, 2021, White Mountains owned 72.0% of Ark on a basic shares outstanding basis (63.0% on a fully-diluted, fully-converted basis, taking account of management’s equity incentives). The remaining shares are owned by employees. In the future, management rollover shareholders could earn additional shares in the company if and to the extent that White Mountains achieves certain multiple of invested capital return thresholds. If fully earned, these additional shares would represent 12.5% of the shares outstanding at closing. See Note 2 — “Significant Transactions”. The NSM segment consists of NSM Insurance HoldCo, LLC and its subsidiaries (collectively, “NSM”). NSM is a full-service managing general underwriting agency (“MGU”) and program administrator for specialty property and casualty insurance. The company places insurance in niche sectors such as specialty transportation, real estate, social services and pet. On behalf of its insurance carrier partners, NSM typically manages all aspects of the placement process, including product development, marketing, underwriting, policy issuance and claims. NSM earns commissions based on the volume and, in some cases, profitability of the insurance that it places. NSM does not take insurance risk. As of September 30, 2021 and December 31, 2020, White Mountains owned 96.6% and 96.5% of the basic units outstanding of NSM (87.3% and 89.6% on a fully diluted, fully converted basis). See Note 2 — “Significant Transactions”. The Kudu segment consists of Kudu Investment Management, LLC and its subsidiaries (collectively “Kudu”). Kudu provides capital solutions for boutique asset managers for a variety of purposes including generational ownership transfers, management buyouts, acquisition and growth finance and legacy partner liquidity. Kudu also provides strategic assistance to investees from time to time. Kudu’s capital solutions typically are structured as minority preferred equity stakes with distribution rights, generally tied to gross revenues and designed to generate immediate strong, stable cash yields. As of September 30, 2021 and December 31, 2020, White Mountains owned 99.3% and 99.1% of the basic units outstanding (84.7% and 85.4% on a fully diluted, fully converted basis). The Other Operations segment consists of the Company and its wholly-owned subsidiary, White Mountains Capital, LLC, (“WM Capital”) its other intermediate holding companies, its wholly-owned investment management subsidiary, White Mountains Advisors LLC (“WM Advisors”), investment assets managed by WM Advisors, its interests in MediaAlpha, Inc. (“MediaAlpha”), PassportCard Limited (“PassportCard”) and DavidShield Life Insurance Agency (2000) Ltd. (“DavidShield”) (collectively, “PassportCard/ DavidShield”), Elementum Holdings LP (“Elementum”), and certain other consolidated and unconsolidated entities and certain other assets. See Note 2 — “Significant Transactions”.
Discontinued Operations and Assets Held for Sale	Discontinued Operations and Assets Held for Sale In the first quarter of 2021, White Mountains recorded a gain on sale of discontinued operations as a result of reversing a liability arising from the tax indemnification provided in connection with the sale of Sirius International Insurance Group, Ltd. (“Sirius Group”) in 2016. On April 12, 2021, NSM sold the Fresh Insurance Services Group Limited (“Fresh Insurance”) motor business, which was classified as held for sale at March 31, 2021. The transaction did not meet the criteria to be classified as discontinued operations. See Note 19 — “Held for Sale and Discontinued Operations”.
Ark Insurance Operations	Ark Insurance Operations Ark writes a diversified portfolio of reinsurance and insurance, including property, marine & energy, specialty, accident & health and casualty, through the Syndicates. Beginning in January 2021, Ark began writing certain classes of its business through GAIL. For the years of account prior to White Mountains’s transaction with Ark, a significant proportion of the Syndicates’ underwriting capital was provided by other third-party insurance and reinsurance groups (“TPC Providers”) using whole account reinsurance contracts through Ark’s corporate member. The TPC Providers’ economic participation in the Syndicates for the remaining open years of account prior to White Mountains’s transaction with Ark is approximately 51% of the total net result of the Syndicates. Captions within results of operations and other comprehensive income are shown net of amounts relating to the TPC Providers share of the Syndicates’ results, including investment results. Ark’s premiums written comprise premiums on insurance contracts incepted during the year as well as premium adjustments related to prior years of account. Insurance premiums are recognized as revenues over the loss exposure or coverage period in proportion to the level of insurance protection provided. In most cases, premiums are earned ratably over the term of the contract with unearned premiums calculated on a monthly pro-rata basis. Catastrophe premiums are earned in proportion to the level of insurance protection provided. Premiums earned are presented net of amounts ceded to reinsurers. Premiums receivable, representing amounts due from insureds, are presented net of an allowance for uncollectible premiums, including expected credit losses, both dispute and credit related. The allowance is based upon Ark’s ongoing review of amounts outstanding, historical loss data, including delinquencies and write-offs, current and forecasted economic conditions and other relevant factors. Credit risk is partially mitigated by Ark’s ability to cancel the policy if the policyholder does not pay the premium. Deferred acquisition costs comprise brokerage and taxes which are directly attributable to and vary with the production of business. These costs are deferred and amortized to the extent they related to successful contract acquisitions over the applicable premium recognition period. Losses and loss adjustment expenses (“LAE”) are charged against income as incurred. Unpaid losses and LAE, including estimates for amounts incurred but not reported (“IBNR”) are based on estimates of the ultimate costs of settling claims, including the effects of inflation and other societal and economic factors. Unpaid loss and LAE reserves represent management’s best estimate of ultimate losses and LAE, net of estimated salvage and subrogation recoveries, if applicable. Such estimates are regularly reviewed and updated and any resulting adjustments are reflected in current results of operations. The process of estimating loss and LAE involves a considerable degree of judgment by management and the ultimate amount of expense to be incurred could be considerably greater than or less than the amounts currently reflected in the financial statements. Reinsurance recoverables represent amounts of paid losses and loss adjustment expenses, case reserves and IBNR amounts ceded to reinsurers under reinsurance treaties. Amounts recoverable from reinsurers are estimated in a manner consistent with the associated claim liability. Ark reports its reinsurance recoverables net of an allowance for estimated uncollectible reinsurance, including expected credit losses. The allowance is based upon its ongoing review of amounts outstanding, length of collection periods, changes in reinsurer credit standing, disputes, applicable coverage defenses and other relevant factors.
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets Goodwill represents the excess of the amount paid to acquire subsidiaries over the fair value of identifiable net assets at the date of acquisition. Other intangible assets consist primarily of underwriting capacity, customer relationships, renewal rights and trade names.
Derivatives	Derivatives From time to time, White Mountains holds derivative financial instruments for risk management purposes. White Mountains recognizes all derivatives as either assets or liabilities, measured at fair value, on the consolidated balance sheet. Changes in the fair value of derivative instruments that meet the criteria for hedge accounting are recognized in other comprehensive income and reclassified into current period pre-tax income when the hedged items are recognized therein. Changes in the fair value of derivative instruments that do not meet the criteria for hedge accounting are recognized in current period pre-tax income. As of September 30, 2021 and December 31, 2020, NSM holds an interest rate swap derivative instrument that meets the criteria for hedge accounting. See Note 9 — “Derivatives”.
Reinsurance Contracts Accounted For As Deposits	Reinsurance Contracts Accounted for as Deposits Reinsurance contracts that do not meet the risk transfer requirements necessary to be accounted for as reinsurance are accounted for using the deposit method. Under the deposit method, ceded premiums paid are not recognized through income but rather treated as a deposit. BAM entered into ceded reinsurance agreements with Fidus Re Ltd. (“Fidus Re”) during the second quarter of 2018 and the first quarter of 2021, which are both accounted for using the deposit method. See Note 10 — “Municipal Bond Guarantee Insurance”. The nonrefundable consideration paid by BAM to Fidus Re is charged to financing expense within general and administrative expenses. Ark has an aggregate excess of loss contract with SiriusPoint Ltd. (“SiriusPoint”), formerly Third Point Reinsurance Ltd., which is accounted for using the deposit method and recorded within other assets. Ark earns an annual crediting rate of 3.0%, which is recorded within other revenue. During the three months ended June 30, 2021, Ark negotiated a reduction of $31.7 million, including accrued interest, to the aggregate excess of loss contract with SiriusPoint. As of September 30, 2021, the carrying value of Ark’s deposit in SiriusPoint, including accrued interest, was $20.3 million.
Cash and Restricted Cash	Cash and Restricted Cash Cash includes amounts on hand and demand deposits with banks and other financial institutions. Amounts presented in the statement of cash flows are shown net of balances acquired and sold in the purchase or sale of the Company’s consolidated subsidiaries. Cash balances that are not immediately available for general corporate purposes, including fiduciary accounts held by NSM on behalf of insurance carriers and the interest reserve account that Kudu maintains under its credit facility, are classified as restricted.

Basis of Presentation and Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2021

The Company is an exempted Bermuda limited liability company whose principal businesses are conducted through its subsidiaries and other affiliates. The Company’s headquarters is located at 26 Reid Street, Hamilton, Bermuda HM 11, its principal executive office is located at 23 South Main Street, Suite 3B, Hanover, New Hampshire 03755-2053 and its registered office is located at Clarendon House, 2 Church Street, Hamilton, Bermuda HM 11. The Company’s website is located at www.whitemountains.com. The information contained on White Mountains’s website is not incorporated by reference into, and is not a part of, this report.

The accompanying consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) and include the accounts of White Mountains Insurance Group, Ltd. (the “Company” or the “Registrant”), its subsidiaries (collectively with the Company, “White Mountains”) and other entities required to be consolidated under GAAP.

Consolidation Principles

Under GAAP, the Company is required to consolidate any entity in which it holds a controlling financial interest. A controlling financial interest is usually in the form of an investment representing the majority of the subsidiary’s voting interests. However, a controlling financial interest may also arise from a financial interest in a variable interest entity (“VIE”) through arrangements that do not involve ownership of voting interests. The Company consolidates a VIE if it determines that it is the primary beneficiary. The primary beneficiary is defined as the entity who holds a variable interest that gives it both the power to direct the VIE’s activities that most significantly impact its economic performance and the obligation to absorb losses of, or the right to receive returns from, the VIE that could potentially be significant to the VIE.

Intercompany transactions have been eliminated in consolidation. These interim financial statements include all adjustments considered necessary by management to fairly state the financial position, results of operations and cash flows of White Mountains. These interim financial statements may not be indicative of financial results for the full year and should be read in conjunction with the Company’s 2020 Annual Report on Form 10-K.

Business Combinations

White Mountains accounts for purchases of businesses using the acquisition method, which requires the measurement of assets acquired, including goodwill and other intangible assets, and liabilities assumed, including contingent liabilities, at their estimated fair values as of the acquisition date. The acquisition date fair values represent management’s best estimates and are based upon established valuation techniques, reasonable assumptions and, where appropriate, valuations performed by independent third parties. In circumstances where additional information is required in order to determine the acquisition date fair value of balance sheet amounts, provisional amounts may be recorded as of the acquisition date and may be subject to subsequent adjustment throughout the measurement period, which is up to one year from the acquisition date. Measurement period adjustments are recognized in the period in which they are determined. The results of operations and cash flows of businesses acquired are included in the consolidated financial statements from the date of acquisition. White Mountains accounts for purchases of other intangible assets that do not meet the definition of a business as asset acquisitions. Asset acquisitions are recognized at the amount of consideration paid, which is deemed to equal fair value.

Use of Estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.

Fair Value Measurements

Fair value measurements are categorized into a hierarchy that distinguishes between inputs based on market data from independent sources (observable inputs) and a reporting entity’s internal assumptions based upon the best information available when external market data is limited or unavailable (unobservable inputs). Quoted prices in active markets for identical assets or liabilities have the highest priority (“Level 1”), followed by observable inputs other than quoted prices, including prices for similar but not identical assets or liabilities (“Level 2”) and unobservable inputs, including the reporting entity’s estimates of the assumptions that market participants would use, having the lowest priority (“Level 3”).

Reportable Segments

White Mountains has determined its reportable segments based on the nature of the underlying businesses, the manner in which the Company’s subsidiaries and affiliates are organized and managed and the organization of the financial information provided to the chief operating decision maker to assess performance and make decisions regarding allocation of resources. As of September 30, 2021, White Mountains’s reportable segments were HG Global/BAM, Ark, NSM, Kudu and Other Operations.

The HG Global/BAM segment consists of HG Global Ltd. and its wholly-owned subsidiaries (“HG Global”) and the consolidated results of Build America Mutual Assurance Company (“BAM”) (collectively, “HG Global/BAM”). BAM is the first and only mutual municipal bond insurance company in the United States. By insuring the timely payment of principal and interest, BAM provides market access to, and lowers interest expense for, issuers of municipal bonds used to finance essential public purposes such as schools, utilities and transportation facilities. BAM is owned by and operated for the benefit of its members, the municipalities that purchase BAM’s insurance for their debt issuances. HG Global was established to fund the startup of BAM and, through its wholly-owned subsidiary, HG Re Ltd. (“HG Re”), to provide up to 15%-of-par, first loss reinsurance protection for policies underwritten by BAM. For capital appreciation bonds, par is adjusted to the estimated equivalent par value for current interest paying bonds. HG Global, together with its subsidiaries, funded the initial capitalization of BAM through the purchase of $503.0 million of surplus notes issued by BAM, consisting of $203.0 million of Series A Notes and $300.0 million of Series B Notes (the “BAM Surplus Notes”). As of September 30, 2021 and December 31, 2020, White Mountains owned 96.9% of HG Global’s preferred equity and 88.4% of its common equity. White Mountains does not have an ownership interest in BAM. However, White Mountains is required to consolidate BAM’s results in its financial statements because BAM is a VIE for which White Mountains is the primary beneficiary. BAM’s results are all attributed to non-controlling interests.

The Ark segment consists of Ark Insurance Holdings Limited and its subsidiaries (collectively, “Ark”). Ark writes a diversified portfolio of reinsurance and insurance, including property, marine & energy, specialty, accident & health and casualty, through Lloyd’s of London (“Lloyd’s”) Syndicates 4020 and 3902 (the “Syndicates”). Beginning in January 2021, Ark began writing certain classes of its business through Group Ark Insurance Limited (“GAIL”), Ark’s wholly-owned Class 4 Bermuda-based insurance and reinsurance company.

As of September 30, 2021, White Mountains owned 72.0% of Ark on a basic shares outstanding basis (63.0% on a fully-diluted, fully-converted basis, taking account of management’s equity incentives). The remaining shares are owned by employees. In the future, management rollover shareholders could earn additional shares in the company if and to the extent that White Mountains achieves certain multiple of invested capital return thresholds. If fully earned, these additional shares would represent 12.5% of the shares outstanding at closing. See Note 2 — “Significant Transactions”.

The NSM segment consists of NSM Insurance HoldCo, LLC and its subsidiaries (collectively, “NSM”). NSM is a full-service managing general underwriting agency (“MGU”) and program administrator for specialty property and casualty insurance. The company places insurance in niche sectors such as specialty transportation, real estate, social services and pet. On behalf of its insurance carrier partners, NSM typically manages all aspects of the placement process, including product development, marketing, underwriting, policy issuance and claims. NSM earns commissions based on the volume and, in some cases, profitability of the insurance that it places. NSM does not take insurance risk. As of September 30, 2021 and December 31, 2020, White Mountains owned 96.6% and 96.5% of the basic units outstanding of NSM (87.3% and 89.6% on a fully diluted, fully converted basis). See Note 2 — “Significant Transactions”.

The Kudu segment consists of Kudu Investment Management, LLC and its subsidiaries (collectively “Kudu”). Kudu provides capital solutions for boutique asset managers for a variety of purposes including generational ownership transfers, management buyouts, acquisition and growth finance and legacy partner liquidity. Kudu also provides strategic assistance to investees from time to time. Kudu’s capital solutions typically are structured as minority preferred equity stakes with distribution rights, generally tied to gross revenues and designed to generate immediate strong, stable cash yields. As of September 30, 2021 and December 31, 2020, White Mountains owned 99.3% and 99.1% of the basic units outstanding (84.7% and 85.4% on a fully diluted, fully converted basis).

The Other Operations segment consists of the Company and its wholly-owned subsidiary, White Mountains Capital, LLC, (“WM Capital”) its other intermediate holding companies, its wholly-owned investment management subsidiary, White Mountains Advisors LLC (“WM Advisors”), investment assets managed by WM Advisors, its interests in MediaAlpha, Inc. (“MediaAlpha”), PassportCard Limited (“PassportCard”) and DavidShield Life Insurance Agency (2000) Ltd. (“DavidShield”) (collectively, “PassportCard/ DavidShield”), Elementum Holdings LP (“Elementum”), and certain other consolidated and unconsolidated entities and certain other assets. See Note 2 — “Significant Transactions”.

Discontinued Operations and Assets Held for Sale

In the first quarter of 2021, White Mountains recorded a gain on sale of discontinued operations as a result of reversing a liability arising from the tax indemnification provided in connection with the sale of Sirius International Insurance Group, Ltd. (“Sirius Group”) in 2016.

On April 12, 2021, NSM sold the Fresh Insurance Services Group Limited (“Fresh Insurance”) motor business, which was classified as held for sale at March 31, 2021. The transaction did not meet the criteria to be classified as discontinued operations. See Note 19 — “Held for Sale and Discontinued Operations”.

Ark Insurance Operations

Ark writes a diversified portfolio of reinsurance and insurance, including property, marine & energy, specialty, accident & health and casualty, through the Syndicates. Beginning in January 2021, Ark began writing certain classes of its business through GAIL.

For the years of account prior to White Mountains’s transaction with Ark, a significant proportion of the Syndicates’ underwriting capital was provided by other third-party insurance and reinsurance groups (“TPC Providers”) using whole account reinsurance contracts through Ark’s corporate member. The TPC Providers’ economic participation in the Syndicates for the remaining open years of account prior to White Mountains’s transaction with Ark is approximately 51% of the total net result of the Syndicates. Captions within results of operations and other comprehensive income are shown net of amounts relating to the TPC Providers share of the Syndicates’ results, including investment results.

Ark’s premiums written comprise premiums on insurance contracts incepted during the year as well as premium adjustments related to prior years of account. Insurance premiums are recognized as revenues over the loss exposure or coverage period in proportion to the level of insurance protection provided. In most cases, premiums are earned ratably over the term of the contract with unearned premiums calculated on a monthly pro-rata basis. Catastrophe premiums are earned in proportion to the level of insurance protection provided. Premiums earned are presented net of amounts ceded to reinsurers. Premiums receivable, representing amounts due from insureds, are presented net of an allowance for uncollectible premiums, including expected credit losses, both dispute and credit related. The allowance is based upon Ark’s ongoing review of amounts outstanding, historical loss data, including delinquencies and write-offs, current and forecasted economic conditions and other relevant factors. Credit risk is partially mitigated by Ark’s ability to cancel the policy if the policyholder does not pay the premium.

Deferred acquisition costs comprise brokerage and taxes which are directly attributable to and vary with the production of business. These costs are deferred and amortized to the extent they related to successful contract acquisitions over the applicable premium recognition period.

Losses and loss adjustment expenses (“LAE”) are charged against income as incurred. Unpaid losses and LAE, including estimates for amounts incurred but not reported (“IBNR”) are based on estimates of the ultimate costs of settling claims, including the effects of inflation and other societal and economic factors. Unpaid loss and LAE reserves represent management’s best estimate of ultimate losses and LAE, net of estimated salvage and subrogation recoveries, if applicable. Such estimates are regularly reviewed and updated and any resulting adjustments are reflected in current results of operations. The process of estimating loss and LAE involves a considerable degree of judgment by management and the ultimate amount of expense to be incurred could be considerably greater than or less than the amounts currently reflected in the financial statements.

Reinsurance recoverables represent amounts of paid losses and loss adjustment expenses, case reserves and IBNR amounts ceded to reinsurers under reinsurance treaties. Amounts recoverable from reinsurers are estimated in a manner consistent with the associated claim liability. Ark reports its reinsurance recoverables net of an allowance for estimated uncollectible reinsurance, including expected credit losses. The allowance is based upon its ongoing review of amounts outstanding, length of collection periods, changes in reinsurer credit standing, disputes, applicable coverage defenses and other relevant factors.

Goodwill and Other Intangible Assets

Goodwill represents the excess of the amount paid to acquire subsidiaries over the fair value of identifiable net assets at the date of acquisition. Other intangible assets consist primarily of underwriting capacity, customer relationships, renewal rights and trade names.

Derivatives

From time to time, White Mountains holds derivative financial instruments for risk management purposes. White Mountains recognizes all derivatives as either assets or liabilities, measured at fair value, on the consolidated balance sheet. Changes in the fair value of derivative instruments that meet the criteria for hedge accounting are recognized in other comprehensive income and reclassified into current period pre-tax income when the hedged items are recognized therein. Changes in the fair value of derivative instruments that do not meet the criteria for hedge accounting are recognized in current period pre-tax income.

As of September 30, 2021 and December 31, 2020, NSM holds an interest rate swap derivative instrument that meets the criteria for hedge accounting. See Note 9 — “Derivatives”.

Reinsurance Contracts Accounted For As Deposits

Reinsurance Contracts Accounted for as Deposits

Reinsurance contracts that do not meet the risk transfer requirements necessary to be accounted for as reinsurance are accounted for using the deposit method. Under the deposit method, ceded premiums paid are not recognized through income but rather treated as a deposit. BAM entered into ceded reinsurance agreements with Fidus Re Ltd. (“Fidus Re”) during the second quarter of 2018 and the first quarter of 2021, which are both accounted for using the deposit method. See Note 10 — “Municipal Bond Guarantee Insurance”. The nonrefundable consideration paid by BAM to Fidus Re is charged to financing expense within general and administrative expenses.

Ark has an aggregate excess of loss contract with SiriusPoint Ltd. (“SiriusPoint”), formerly Third Point Reinsurance Ltd., which is accounted for using the deposit method and recorded within other assets. Ark earns an annual crediting rate of 3.0%, which is recorded within other revenue. During the three months ended June 30, 2021, Ark negotiated a reduction of $31.7 million, including accrued interest, to the aggregate excess of loss contract with SiriusPoint. As of September 30, 2021, the carrying value of Ark’s deposit in SiriusPoint, including accrued interest, was $20.3 million.

Cash and Restricted Cash

Cash includes amounts on hand and demand deposits with banks and other financial institutions. Amounts presented in the statement of cash flows are shown net of balances acquired and sold in the purchase or sale of the Company’s consolidated subsidiaries.

Cash balances that are not immediately available for general corporate purposes, including fiduciary accounts held by NSM on behalf of insurance carriers and the interest reserve account that Kudu maintains under its credit facility, are classified as restricted.