Investments Maturity Distribution of Debt Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, within One Year, Amortized Cost Basis	$ 122,544
Available-for-sale Securities, Debt Maturities, after One through Five Years, Amortized Cost Basis	106,106
Available-for-sale Securities, Debt Maturities, after Five through Ten years, Amortized Cost Basis	215,718
Debt Securities, Available-for-sale, Allocated and Single Maturity Date, Maturity, after 10 Years, Amortized Cost	849,485
Debt Securities, Available-for-sale, Amortized Cost	1,293,853	$ 1,223,747
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, within One Year, Fair Value	123,391
Available-for-sale Securities, Debt Maturities, after One through Five Years, Fair Value	111,107
Available-for-sale Securities, Debt Maturities, after Five through Ten Years, Fair Value	230,069
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after 10 Years, Fair Value	913,392
Debt Securities, Available-for-sale	$ 1,377,959	$ 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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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in second through fifth fiscal year following latest fiscal year. Excludes interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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Amount 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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