Securities (Scheduled Contractual Maturities of AFS Debt Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Amortized Cost
Due within one year	$ 893,162
Due after one year through five years	639,543
Due after five years through ten years	483,606
Due after ten years	3,454,212
Amortized Cost	5,470,523	$ 3,320,648
Fair Value
Due within one year	892,648
Due after one year through five years	646,245
Due after five years through ten years	499,880
Due after ten years	3,505,885
Total available-for-sale Debt securities	5,544,658	3,317,214
Available-for-sale debt securities pledged as collateral at fair value	$ 588,484	$ 479,432