Investment Securities (Details 2) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Amortized Cost
Due in one year or less	$ 10,384
Due after one year through five years	486,326
Due after five years through ten years	1,053,610
Due after ten years	2,268,389
Total securities available-for-sale	3,818,709	$ 3,721,525
Fair Value
Due in one year or less	10,517
Due after one year through five years	483,913
Due after five years through ten years	1,035,714
Due after ten years	2,271,842
Total securities available-for-sale	$ 3,801,986	$ 3,774,431