Investment Securities - Schedule Of Amortized Cost And Fair Value By Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
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	9,889
After 10 years	0
Subtotal	9,889
Government agency issued MBS and CMO	0
Securities held to maturity, fair value	9,889	9,843
Available-for-Sale, Amortized Cost
Within 1 year	15,060
After 1 year; within 5 years	229,373
After 5 years; within 10 years	755
After 10 years	37,273
Subtotal	282,461
Government agency issued MBS and CMO	4,356,706
Securities available for sale, amortized cost	4,639,167
Available-for-Sale, Fair Value
Within 1 year	14,998
After 1 year; within 5 years	231,160
After 5 years; within 10 years	3,825
After 10 years	48,746
Subtotal	298,729
Government agency issued MBS and CMO	4,317,593
Securities available-for-sale	$ 4,616,322	$ 4,626,470