Securities, AFS Debt Securities, Contractual Maturities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Available-for-sale Securities, Debt Maturities, Amortized Cost [Abstract]
Within one year	$ 1,258
From one to five years	56,017
From five to ten years	642,112
After ten years	867,985
Amortized cost	1,567,372	$ 1,318,711
Available-for-sale Securities, Debt Maturities, Estimated Fair Value [Abstract]
Within one year	1,262
From one to five years	56,596
From five to ten years	639,238
After ten years	878,934
Fair value	$ 1,576,030	$ 1,348,698