Investments (Maturity Distribution) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale, Amortized Cost
Due in one year or less	$ 25,079
Available-for-sale Securities, Debt Maturities, Due After One Year Through Five Years, Amortized Cost Basis	114,900
Available-for-sale Securities, Debt Maturities, Due After Five Years Through Ten Years, Amortized Cost Basis	214,052
Available-for-sale Securities, Debt Maturities, Due After Ten Years, Amortized Cost Basis	978,601
Debt Securities, Available-for-sale, Amortized Cost	1,332,632	$ 1,321,487
Debt Securities, Available-for-sale, Fair Value
Due in one year or less	25,438
Available-for-sale Securities, Debt Maturities, Due After One Year Through Five Years, Fair Value	125,058
Available-for-sale Securities, Debt Maturities, Due After Five Years Through Ten Years, Fair Value	231,241
Available-for-sale Securities, Debt Maturities, Due After Ten Years, Fair Value	1,038,850
Debt Securities, Available-for-sale	$ 1,420,587	$ 1,489,383

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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