Investments (Maturity Distribution) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale, Amortized Cost
Due in one year or less	$ 109,032
Available-for-sale Securities, Debt Maturities, Due After One Year Through Five Years, Amortized Cost Basis	113,913
Available-for-sale Securities, Debt Maturities, Due After Five Years Through Ten Years, Amortized Cost Basis	215,501
Available-for-sale Securities, Debt Maturities, Due After Ten Years, Amortized Cost Basis	876,461
Debt Securities, Available-for-sale, Amortized Cost	1,314,907	$ 1,293,853
Debt Securities, Available-for-sale, Fair Value
Due in one year or less	109,456
Available-for-sale Securities, Debt Maturities, Due After One Year Through Five Years, Fair Value	116,458
Available-for-sale Securities, Debt Maturities, Due After Five Years Through Ten Years, Fair Value	222,473
Available-for-sale Securities, Debt Maturities, Due After Ten Years, Fair Value	907,857
Debt Securities, Available-for-sale	$ 1,356,244	$ 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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