Investment Securities - Schedule Of Amortized Cost And Fair Value By Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 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	9,987
After 10 years	0
Subtotal	9,987
Government agency issued MBS and CMO	0
Securities held to maturity, fair value	9,987	9,843
Available-for-Sale, Amortized Cost
Within 1 year	20,161
After 1 year; within 5 years	223,908
After 5 years; within 10 years	755
After 10 years	79,453
Subtotal	324,277
Government agency issued MBS and CMO	4,025,914
Securities available for sale, amortized cost	4,350,191
Available-for-Sale, Fair Value
Within 1 year	20,289
After 1 year; within 5 years	228,037
After 5 years; within 10 years	2,444
After 10 years	96,423
Subtotal	347,193
Government agency issued MBS and CMO	4,068,652
Securities available-for-sale	$ 4,415,845	$ 4,626,470