Investments (Maturity Distribution) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale, Amortized Cost
Due in one year or less	$ 102,787
Available-for-sale Securities, Debt Maturities, Due After One Year Through Five Years, Amortized Cost Basis	131,248
Available-for-sale Securities, Debt Maturities, Due After Five Years Through Ten Years, Amortized Cost Basis	214,674
Available-for-sale Securities, Debt Maturities, Due After Ten Years, Amortized Cost Basis	825,376
Debt Securities, Available-for-sale, Amortized Cost	1,274,085	$ 1,223,747
Debt Securities, Available-for-sale, Fair Value
Due in one year or less	103,200
Available-for-sale Securities, Debt Maturities, Due After One Year Through Five Years, Fair Value	136,348
Available-for-sale Securities, Debt Maturities, Due After Five Years Through Ten Years, Fair Value	226,791
Available-for-sale Securities, Debt Maturities, Due After Ten Years, Fair Value	875,000
Debt Securities, Available-for-sale	$ 1,341,339	$ 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).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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