Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	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