Investment Securities (Details 2) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Amortized Cost
Due in one year or less	$ 20,945
Due after one year through five years	594,720
Due after five years through ten years	997,539
Due after ten years	2,275,885
Total securities available-for-sale	3,889,089	$ 3,721,525
Fair Value
Due in one year or less	21,035
Due after one year through five years	589,860
Due after five years through ten years	971,186
Due after ten years	2,275,707
Total securities available-for-sale	$ 3,857,788	$ 3,774,431