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Investments - Net Effect on Stockholders' Equity of Unrealized Gains and Losses on Available-for-sale Securities (Parenthetical) (Details) $ in Millions	Dec. 31, 2017 USD ($)
Prior to adoption of ASU 2016-01 [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Net unrealized gains for equity securities recognized in accumulated other comprehensive income (loss) prior to adoption of ASU 2016-01	$ 9.8

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- Definition

Accumulated other comprehensive income loss available for sale equity securities adjustment net of tax.

+ References

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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.

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No definition available.

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