Investment Securities - Schedule Of Amortized Cost And Fair Value By Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Available-for-Sale, Amortized Cost
Within 1 year	$ 453,324
After 1 year; within 5 years	192,172
After 5 years; within 10 years	152,870
After 10 years	607,689
Subtotal	1,406,055
Government agency issued MBS and CMO	6,406,682
Securities available for sale, amortized cost	7,812,737
Available-for-Sale, Fair Value
Securities available-for-sale	7,995,872	$ 4,445,403
Securities available-for-sale, excluding interest only strip:
Available-for-Sale, Amortized Cost
Securities available for sale, amortized cost	7,812,737	4,385,003
Available-for-Sale, Fair Value
Within 1 year	455,069
After 1 year; within 5 years	196,096
After 5 years; within 10 years	160,078
After 10 years	619,157
Subtotal	1,430,400
Government agency issued MBS and CMO	6,532,513
Securities available-for-sale	$ 7,962,913	$ 4,426,267