Securities (Schedule of Contractual Maturities of Investment Securities Available for Sale) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Abstract]
Due within one year, Amortized Cost	$ 81,385
Due after one year through five years, Amortized Cost	737,066
Due after five years through ten years, Amortized Cost	2,457,820
Due after ten years, Amortized Cost	2,141,102
Debt securities available-for-sale, amortized cost	5,417,373	$ 4,997,529
Due within one year, Fair Value	81,986
Due after one year through five years, Fair Value	765,090
Due after five years through ten years, Fair Value	2,507,546
Due after ten years, Fair Value	2,141,668
Debt securities available for sale at fair value	$ 5,496,290	$ 5,210,134

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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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 sixth through tenth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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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 current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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