Investment Securities - Schedule Of Amortized Cost And Fair Value By Contractual Maturity (Details) - USD ($) $ in Thousands	Jun. 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	9,923
After 10 years	0
Subtotal	9,923
Government agency issued MBS and CMO	0
Securities held to maturity, fair value	9,923	9,843
Available-for-Sale, Amortized Cost
Within 1 year	0
After 1 year; within 5 years	244,114
After 5 years; within 10 years	755
After 10 years	44,426
Subtotal	289,295
Government agency issued MBS and CMO	4,080,552
Securities available for sale, amortized cost	4,369,847
Available-for-Sale, Fair Value
Within 1 year	0
After 1 year; within 5 years	248,270
After 5 years; within 10 years	4,036
After 10 years	61,436
Subtotal	313,742
Government agency issued MBS and CMO	4,101,867
Securities available-for-sale	$ 4,415,609	$ 4,626,470