Investments (Maturity Distribution) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale, Amortized Cost
Due in one year or less	$ 47,918
Available-for-sale Securities, Debt Maturities, Due After One Year Through Five Years, Amortized Cost Basis	106,727
Available-for-sale Securities, Debt Maturities, Due After Five Years Through Ten Years, Amortized Cost Basis	227,840
Available-for-sale Securities, Debt Maturities, Due After Ten Years, Amortized Cost Basis	925,571
Debt Securities, Available-for-sale, Amortized Cost	1,308,056	$ 1,293,853
Debt Securities, Available-for-sale, Fair Value
Due in one year or less	48,263
Available-for-sale Securities, Debt Maturities, Due After One Year Through Five Years, Fair Value	114,430
Available-for-sale Securities, Debt Maturities, Due After Five Years Through Ten Years, Fair Value	250,142
Available-for-sale Securities, Debt Maturities, Due After Ten Years, Fair Value	1,031,744
Debt Securities, Available-for-sale	$ 1,444,579	$ 1,377,959

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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