Investment Securities - Schedule Of Amortized Cost And Fair Value By Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Held-to-Maturity, Amortized Cost
Within 1 year	$ 0
After 1 year; within 5 years	0
After 5 years; within 10 years	10,000
After 10 years	0
Subtotal	10,000
Government agency issued MBS and CMO	0
Total	10,000	$ 10,000
Held-to-Maturity, Fair Value
Within 1 year	0
After 1 year; within 5 years	0
After 5 years; within 10 years	9,824
After 10 years	0
Subtotal	9,824
Government agency issued MBS and CMO	0
Securities held to maturity, fair value	9,824	10,001
Available-for-Sale, Amortized Cost
Within 1 year	54,958
After 1 year; within 5 years	189,021
After 5 years; within 10 years	3,581
After 10 years	233,571
Subtotal	481,131
Government agency issued MBS and CMO	3,882,343
Securities available for sale, amortized cost	4,363,474
Available-for-Sale, Fair Value
Within 1 year	55,730
After 1 year; within 5 years	195,624
After 5 years; within 10 years	8,480
After 10 years	255,613
Subtotal	515,447
Government agency issued MBS and CMO	4,029,460
Securities available-for-sale	$ 4,544,907	$ 4,445,403