Investment Securities (Details 2) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investment Securities, Available-for-Sale, Amortized Cost
Due in one year or less	$ 14,398
Due after one year through five years	375,559
Due after five years through ten years	1,128,639
Due after ten years	2,202,929
Total	3,721,525	$ 3,213,655
Investment Securities, Available-for-Sale, Estimated Fair Value
Due in one year or less	15,091
Due after one year through five years	378,522
Due after five years through ten years	1,130,138
Due after ten years	2,250,680
Securities available‑for‑sale	$ 3,774,431	$ 3,223,830