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Summary of Significant Accounting Policies - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2023 USD ($) Country Segment Facility shares | Dec. 31, 2022 USD ($) | Dec. 31, 2021 USD ($)
Significant Accounting Policies [Line Items] |  |  |
Number of reportable segments | Segment | 3 |  |
Number of commercial clean coal production facilities | Facility | 35 |  |
Number of countries in which the company does business through a network of correspondent brokers and consultants | Country | 130 |  |
Percentage of variable ownership interest | 50.00% |  |
Description of contracts renewal period | one year or less |  |
Percentage of commission and fee revenues on the effective date | 80.00% |  |
Percentage of commission and fee revenues in the first three months | 15.00% |  |
Percentage of commission and fee revenues after the first three months | 5.00% |  |
Allowances for estimated policy cancellations | $ 9,900,000 | $ 9,300,000 |
Allowance for doubtful accounts | $ 23,000,000 | 11,100,000 |
Premium financing contracts, terms | premium financing contracts are structured to minimize potential bad debt expense to us. Such receivables are generally considered delinquent after seven days of the payment due date. In normal course, insurance policies are canceled within one month of the contractual payment due date if the payment remains delinquent. |  |
Outstanding loan receivable | $ 685,700,000 | 546,300,000 |
Write-off of amortizable intangible assets | $ 3,500,000 | $ 2,000,000.0 | $ 17,600,000
Impairment, Intangible Asset, Finite-Lived, Statement of Income or Comprehensive Income [Extensible Enumeration] | Depreciation, Amortization and Accretion, Net | Depreciation, Amortization and Accretion, Net | Depreciation, Amortization and Accretion, Net
Employee Stock Purchase Plan [Member] |  |  |
Significant Accounting Policies [Line Items] |  |  |
Shares authorized | shares | 8,000,000.0 |  |
Percentage of employees contribution | 15.00% |  |
Purchase price of common stock, percentage | 95.00% |  |
Aggregate fair market value of shares purchased | $ 25,000 |  |
Maximum number of shares purchased by employees | shares | 2,000 |  |
Shares available for grant | shares | 5,000,000 |  |
Maximum [Member] | Partially Owned Entities [Member] |  |  |
Significant Accounting Policies [Line Items] |  |  |
Percentage of ownership interest | 50.00% |  |
Maximum [Member] | Expiration Lists [Member] |  |  |
Significant Accounting Policies [Line Items] |  |  |
Estimated useful lives of intangibles assets, years | 15 years |  |
Maximum [Member] | Non-Compete Agreements [Member] |  |  |
Significant Accounting Policies [Line Items] |  |  |
Estimated useful lives of intangibles assets, years | 6 years |  |
Maximum [Member] | Trade Names [Member] |  |  |
Significant Accounting Policies [Line Items] |  |  |
Estimated useful lives of intangibles assets, years | 15 years |  |
Minimum [Member] | Majority-owned Subsidiaries [Member] |  |  |
Significant Accounting Policies [Line Items] |  |  |
Percentage of ownership interest | 50.00% |  |
Minimum [Member] | Expiration Lists [Member] |  |  |
Significant Accounting Policies [Line Items] |  |  |
Estimated useful lives of intangibles assets, years | 2 years |  |
Minimum [Member] | Non-Compete Agreements [Member] |  |  |
Significant Accounting Policies [Line Items] |  |  |
Estimated useful lives of intangibles assets, years | 2 years |  |
Minimum [Member] | Trade Names [Member] |  |  |
Significant Accounting Policies [Line Items] |  |  |
Estimated useful lives of intangibles assets, years | 2 years |  |

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