Investment Securities - Debt Maturities (Details) - Investment securities: - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Amortized Cost
Due within one year	$ 678,261
Due after one year through five years	845,628
Due after five years through ten years	1,446,607
Due after ten years	713,570
Debt securities, available-for-sale, amortized cost	3,684,066	$ 3,843,666
Fair Value
Due within one year	678,387
Due after one year through five years	846,303
Due after five years through ten years	1,450,446
Due after ten years	721,068
Total, Fair Value	$ 3,696,204	$ 3,853,692
Weighted- Average Yield
Due within one year	1.64%
Due after one year through five years	0.55%
Due after five years through ten years	0.64%
Due after ten years	0.64%
Total, Weighted-Average Yield	0.81%