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Summary of Significant Accounting Policies - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2018 USD ($) Country Segment shares | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($)
Significant Accounting Policies [Line Items] |  |  |
Number of reportable operating segments | Segment | 3 |  |
Number of commercial clean coal production facilities | 34 |  |
Number of countries in which the company has operations | Country | 35 |  |
Number of countries in which the company does business through a network of correspondent brokers and consultants | Country | 150 |  |
Percentage of ownership interest | 50.00% |  |
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% |  |
Maturity period of short-term investments | 90 days or less |  |
Allowances for estimated policy cancellations | $ 7,800,000 | $ 7,400,000 |
Allowance for doubtful accounts | $ 10,000,000 | 13,500,000 |
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 cancelled within one month of the contractual payment due date if the payment remains delinquent. |  |
Outstanding loan receivable | $ 316,200,000 | 305,500,000 |
Write-off of amortizable intangible assets | $ 10,600,000 | $ 6,200,000 | $ 1,800,000
Minimum [Member] |  |  |
Significant Accounting Policies [Line Items] |  |  |
Percentage of ownership interest | 1.00% |  |
Maximum [Member] |  |  |
Significant Accounting Policies [Line Items] |  |  |
Percentage of ownership interest | 50.00% |  |
Employee Stock Purchase Plan [Member] |  |  |
Significant Accounting Policies [Line Items] |  |  |
Shares authorized | shares | 8,000,000 |  |
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 | 6,800,000 |  |
Expiration Lists [Member] | Minimum [Member] |  |  |
Significant Accounting Policies [Line Items] |  |  |
Estimated useful lives of intangibles assets, years | 2 years |  |
Expiration Lists [Member] | Maximum [Member] |  |  |
Significant Accounting Policies [Line Items] |  |  |
Estimated useful lives of intangibles assets, years | 15 years |  |
Non-Compete Agreements [Member] | Minimum [Member] |  |  |
Significant Accounting Policies [Line Items] |  |  |
Estimated useful lives of intangibles assets, years | 3 years |  |
Non-Compete Agreements [Member] | Maximum [Member] |  |  |
Significant Accounting Policies [Line Items] |  |  |
Estimated useful lives of intangibles assets, years | 5 years |  |
Trade Names [Member] | Minimum [Member] |  |  |
Significant Accounting Policies [Line Items] |  |  |
Estimated useful lives of intangibles assets, years | 2 years |  |
Trade Names [Member] | Maximum [Member] |  |  |
Significant Accounting Policies [Line Items] |  |  |
Estimated useful lives of intangibles assets, years | 15 years |  |

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