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Concentration of Credit Risk - Additional Information (Detail) - Credit Concentration Risk [Member] $ in Millions	Dec. 31, 2018 USD ($)
Corporate Bonds [Member]
Concentration Risk [Line Items]
Fair value of financial instruments	$ 181.8
Mortgage Backed Securities [Member]
Concentration Risk [Line Items]
Fair value of financial instruments	87.9
U.S. Treasuries [Member]
Concentration Risk [Line Items]
Fair value of financial instruments	45.2
U.S. Government Agency Securities [Member]
Concentration Risk [Line Items]
Fair value of financial instruments	$ 44.7

X

- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

No definition available.

+ Details

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X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Details

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X

- Details

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Balance Type:
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X

- Details

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X

- Details

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X

- Details

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