Investment Securities - Debt Maturities (Details) - Debt Securities - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Amortized Cost
Due within one year	$ 1,226,467
Due after one year through five years	271,300
Due after five years through ten years	788,901
Due after ten years	674,762
Amortized Cost	2,961,430	$ 2,222,920
Fair Value
Due within one year	1,227,930
Due after one year through five years	270,938
Due after five years through ten years	786,549
Due after ten years	674,426
Total	$ 2,959,843	$ 2,217,852
Weighted- Average Yield
Due within one year	1.57%
Due after one year through five years	2.19%
Due after five years through ten years	2.15%
Due after ten years	2.49%
Total	1.99%