Investment Securities - Debt Maturities (Details) - Investment Securities [Member] - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Amortized Cost
Due within one year	$ 1,265,454
Due after one year through five years	212,838
Due after five years through ten years	761,882
Due after ten years	679,985
Amortized Cost	2,920,159	$ 2,222,920
Fair Value
Due within one year	1,267,431
Due after one year through five years	212,891
Due after five years through ten years	760,584
Due after ten years	681,598
Total	$ 2,922,504	$ 2,217,852
Weighted- Average Yield
Due within one year	1.41%
Due after one year through five years	2.89%
Due after five years through ten years	2.84%
Due after ten years	3.01%
Total	2.26%