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Concentration of Credit Risk - Additional Information (Detail) - Credit Concentration Risk [Member] $ in Millions | Dec. 31, 2019 USD ($)
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Corporate Bonds [Member] |
Concentration Risk [Line Items] |
Fair value of financial instruments | $ 154.1
Mortgage Backed Securities [Member] |
Concentration Risk [Line Items] |
Fair value of financial instruments | 66.5
Money Market Funds [Member] |
Concentration Risk [Line Items] |
Fair value of financial instruments | 64.6
U.S. Government Agency Securities [Member] |
Concentration Risk [Line Items] |
Fair value of financial instruments | 36.2
U.S. Treasuries [Member] |
Concentration Risk [Line Items] |
Fair value of financial instruments | 21.4
Asset Backed Securities [Member] |
Concentration Risk [Line Items] |
Fair value of financial instruments | $ 14.3

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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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