Investment Securities - Debt Maturities (Details) - Investment Securities [Member] - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Amortized Cost
Due within one year	$ 1,386,034
Due after one year through five years	255,262
Due after five years through ten years	774,103
Due after ten years	695,947
Amortized Cost	3,111,346	$ 2,222,920
Fair Value
Due within one year	1,387,726
Due after one year through five years	254,904
Due after five years through ten years	772,428
Due after ten years	696,574
Total	$ 3,111,632	$ 2,217,852
Weighted- Average Yield
Due within one year	1.37%
Due after one year through five years	2.49%
Due after five years through ten years	2.51%
Due after ten years	2.75%
Total	2.06%