Securities, AFS Debt Securities, Contractual Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Available-for-sale Securities, Debt Maturities, Amortized Cost [Abstract]
Within one year	$ 268
From one to five years	28,692
From five to ten years	170,771
After ten years	768,823
Amortized cost	968,554	$ 1,017,626
Available-for-sale Securities, Debt Maturities, Estimated Fair Value [Abstract]
Within one year	272
From one to five years	28,668
From five to ten years	171,943
After ten years	774,457
Fair value	$ 975,340	$ 998,496