Securities, AFS Debt Securities, Contractual Maturities (Details) $ in Thousands	Sep. 30, 2018 USD ($)
Available-for-sale Securities, Debt Maturities, Amortized Cost [Abstract]
Within one year	$ 46,641
From one to five years	86,348
From five to ten years	176,260
After ten years	832,196
Amortized cost	1,141,445
Available-for-sale Securities, Debt Maturities, Estimated Fair Value [Abstract]
Within one year	46,521
From one to five years	84,188
From five to ten years	171,240
After ten years	799,125
Fair value	$ 1,101,074