Investment Securities - Contractual Maturities of Securities Available-for-Sale (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Amortized Cost
Due in one year or less	$ 8,979
Due after one year through five years	328,227
Due after five years through ten years	967,544
Due after ten years	2,345,229
Total securities available-for-sale	3,649,979	$ 3,688,091
Fair Value
Due in one year or less	9,110
Due after one year through five years	344,634
Due after five years through ten years	1,032,710
Due after ten years	2,464,687
Total securities available-for-sale	$ 3,851,141	$ 3,797,187