Fair Value Measurements Disclosure [Line Items]

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- Definition

Notes receivable interest rate, stated percentage

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Number of Available for Sale Securities

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Number of Credit Agreement

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- Definition

Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

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- Definition

For an unclassified balance sheet, amounts due from parties associated with the reporting entity as evidenced by a written promise to pay.

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- Definition

Amount of investments classified as other.

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Includes other investments and securities that are not at fair value as of the balance sheet date and those that are not accounted for under the equity method.

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Fair Value of Financial Instruments - Additional Information (Detail) $ in Millions	1 Months Ended		9 Months Ended
	May 31, 2019 Agreement	May 31, 2009 Agreement	Sep. 30, 2019	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Fair Value Measurements Disclosure [Line Items]
Other invested assets				$ 62.5	$ 69.7
Other invested assets, at cost				12.5	6.5
Number of Credit Agreements \| Agreement	2	2
Notes receivable from affiliate				70.0	70.0
Level 3 [Member]
Fair Value Measurements Disclosure [Line Items]
Federal home loan bank stock				12.0
Other invested assets, at cost				$ 0.5
International funds [Member]
Fair Value Measurements Disclosure [Line Items]
Number of available for sale securities				1
Other invested assets				$ 48.5	$ 56.4
Affiliated Entity [Member]
Fair Value Measurements Disclosure [Line Items]
Notes receivable from affiliate				$ 70.0
Affiliated Entity [Member] \| Level 2 [Member]
Fair Value Measurements Disclosure [Line Items]
Notes receivable interest rate (percent)			7.00%