Securities, AFS Debt Securities, Contractual Maturities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Available-for-sale Securities, Debt Maturities, Amortized Cost [Abstract]
Within one year	$ 123
From one to five years	52,233
From five to ten years	174,204
After ten years	747,740
Amortized cost	974,300	$ 1,017,626
Available-for-sale Securities, Debt Maturities, Estimated Fair Value [Abstract]
Within one year	123
From one to five years	52,196
From five to ten years	175,628
After ten years	751,749
Fair value	$ 979,696	$ 998,496