Investment Securities - Schedule Of Amortized Cost And Fair Value By Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Held-to-maturity, Amortized Cost [Abstract]
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
Amortized Cost	10,000	$ 10,000
Held-to-maturity, Fair Value [Abstract]
Within 1 year	0
After 1 year; within 5 years	0
After 5 years; within 10 years	10,001
After 10 years	0
Subtotal	10,001
Government agency issued MBS and CMO	0
Fair Value	10,001	9,843
Available-for-sale, Amortized Cost [Abstract]
Within 1 year	35,022
After 1 year; within 5 years	209,003
After 5 years; within 10 years	755
After 10 years	156,069
Subtotal, Amortized Cost	400,849
Government agency issued MBS and CMO	3,984,154
Securities available for sale, amortized cost	4,385,003
Available-for-sale, Fair Value [Abstract]
Within 1 year	35,211
After 1 year; within 5 years	213,108
After 5 years; within 10 years	3,332
After 10 years	174,743
Subtotal, Fair Value	426,394
Government agency issued MBS and CMO	4,019,009
Securities available for sale, fair value	$ 4,445,403	$ 4,626,470