Investment Securities - Debt Maturities (Details) - Debt Securities - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Amortized Cost
Due within one year	$ 1,235,047
Due after one year through five years	364,971
Due after five years through ten years	922,322
Due after ten years	936,617
Amortized Cost	3,458,957	$ 2,961,430
Fair Value
Due within one year	1,241,040
Due after one year through five years	364,927
Due after five years through ten years	926,675
Due after ten years	934,736
Total	$ 3,467,378	$ 2,959,843
Weighted- Average Yield
Due within one year	1.58%
Due after one year through five years	0.99%
Due after five years through ten years	0.72%
Due after ten years	0.69%
Total	1.05%