Investment Securities - Debt Maturities (Details) - Investment securities: $ in Thousands	Mar. 31, 2022 USD ($)
Amortized Cost
Due within one year	$ 795,326
Due after one year through five years	940,430
Due after five years through ten years	1,862,354
Due after ten years	660,117
Debt securities, available-for-sale, amortized cost	4,258,227
Fair Value
Due within one year	790,653
Due after one year through five years	927,942
Due after five years through ten years	1,812,438
Due after ten years	664,281
Total, Fair Value	$ 4,195,314
Weighted- Average Yield
Due within one year	0.79%
Due after one year through five years	0.42%
Due after five years through ten years	0.96%
Due after ten years	0.71%
Total, Weighted-Average Yield	0.77%