Investment Securities - Debt Maturities (Details) - Investment securities: - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Amortized Cost
Due within one year	$ 977,778
Due after one year through five years	711,832
Due after five years through ten years	1,362,956
Due after ten years	765,012
Debt securities, available-for-sale, amortized cost	3,817,578	$ 3,843,666
Fair Value
Due within one year	977,976
Due after one year through five years	712,720
Due after five years through ten years	1,368,656
Due after ten years	772,880
Total, Fair Value	$ 3,832,232	$ 3,853,692
Weighted- Average Yield
Due within one year	1.82%
Due after one year through five years	0.61%
Due after five years through ten years	0.52%
Due after ten years	0.63%
Total, Weighted-Average Yield	0.89%