Securities, AFS Debt Securities, Contractual Maturities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Available-for-sale Securities, Debt Maturities, Amortized Cost [Abstract]
Within one year	$ 37
From one to five years	30,404
From five to ten years	171,485
After ten years	722,511
Amortized cost	924,437	$ 1,017,626
Available-for-sale Securities, Debt Maturities, Estimated Fair Value [Abstract]
Within one year	37
From one to five years	30,393
From five to ten years	173,220
After ten years	728,523
Fair value	$ 932,173	$ 998,496