Investment Securities - Debt Maturities (Details) - Investment securities - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Amortized Cost
Due within one year	$ 1,142,369
Due after one year through five years	361,971
Due after five years through ten years	1,129,147
Due after ten years	889,187
Amortized Cost	3,522,674	$ 2,961,430
Fair Value
Due within one year	1,146,222
Due after one year through five years	362,065
Due after five years through ten years	1,134,255
Due after ten years	889,648
Total	$ 3,532,190	$ 2,959,843
Weighted- Average Yield
Due within one year	2.01%
Due after one year through five years	0.76%
Due after five years through ten years	0.67%
Due after ten years	0.69%
Total	1.12%