Securities (Amortized Cost and Fair Value of Debt Securities by Contractual Maturity) (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Investments Debt And Equity Securities [Abstract]
Debt Securities Available for Sale, Due in one year or less, Amortized Cost	$ 691
Debt Securities Available for Sale, Due after one year through five years, Amortized Cost	687,364
Debt Securities Available for Sale, Due after five years through ten years, Amortized Cost	2,902,497
Debt Securities Available for Sale, Due after ten years, Amortized Cost	2,789,450
Securities Available for Sale, Gross Amortized Cost	6,380,002	$ 6,984,530
Debt Securities Available for Sale, Due in one year or less, Fair Value	694
Debt Securities Available for Sale, Due after one year through five years, Fair Value	681,925
Debt Securities Available for Sale, Due after five years through ten years, Fair Value	2,715,517
Debt Securities Available for Sale, Due after ten years, Fair Value	2,594,871
Total available for sale debt securities, Fair Value	5,993,007	6,986,698
Debt Securities Held to Maturity, Due in one year or less, Amortized Cost	11,225
Debt Securities Held to Maturity, Due after one year through five years, Amortized Cost	379,981
Debt Securities Held to Maturity, Due after five years through ten years, Amortized Cost	891,327
Debt Securities Held to Maturity, Due after ten years, Amortized Cost	1,205,555
Total held to maturity debt securities, Amortized Cost	2,488,088	1,565,751
Debt Securities Held to Maturity, Due in one year or less, Fair Value	11,248
Debt Securities Held to Maturity, Due after one year through five years, Fair Value	379,671
Debt Securities Held to Maturity, Due after five years through ten years, Fair Value	873,478
Debt Securities Held to Maturity, Due after ten years, Fair Value	1,164,652
Total held to maturity debt securities, Fair Value	$ 2,429,049	$ 1,631,482