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Concentration of Credit Risk - Additional Information (Detail) - Credit Concentration Risk [Member] $ in Millions | Dec. 31, 2018 USD ($)
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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

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- 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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- 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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