Investments (Maturity Distribution) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale, Amortized Cost
Due in one year or less	$ 111,775
Available-for-sale Securities, Debt Maturities, Due After One Year Through Five Years, Amortized Cost Basis	118,968
Available-for-sale Securities, Debt Maturities, Due After Five Years Through Ten Years, Amortized Cost Basis	198,215
Available-for-sale Securities, Debt Maturities, Due After Ten Years, Amortized Cost Basis	849,335
Debt Securities, Available-for-sale, Amortized Cost	1,278,293	$ 1,223,747
Debt Securities, Available-for-sale, Fair Value
Due in one year or less	112,511
Available-for-sale Securities, Debt Maturities, Due After One Year Through Five Years, Fair Value	124,385
Available-for-sale Securities, Debt Maturities, Due After Five Years Through Ten Years, Fair Value	212,237
Available-for-sale Securities, Debt Maturities, Due After Ten Years, Fair Value	920,515
Debt Securities, Available-for-sale	$ 1,369,648	$ 1,231,039

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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