Investment Securities - Debt Maturities (Details) - Investment Securities [Member] - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Amortized Cost
Due within one year	$ 982,026
Due after one year through five years	272,477
Due after five years through ten years	650,974
Due after ten years	557,498
Amortized Cost	2,462,975	$ 2,222,920
Fair Value
Due within one year	982,554
Due after one year through five years	272,528
Due after five years through ten years	647,882
Due after ten years	555,014
Total	$ 2,457,978	$ 2,217,852
Weighted- Average Yield
Due within one year	1.40%
Due after one year through five years	2.78%
Due after five years through ten years	2.87%
Due after ten years	3.08%
Total	2.32%