Securities (Details 5) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Amortized Cost
Due within one year	$ 519,223
Due after one year through five years	878,436
Due after five years through ten years	241,665
Due after ten years	1,366,109
Total available-for-sale investment securities	3,005,433
Estimated Fair Value
Due within one year	503,271
Due after one year through five years	867,870
Due after five years through ten years	236,183
Due after ten years	1,354,710
Total available-for-sale investment securities	2,962,034	$ 3,335,795
Amortized Cost
Due after ten years	132,497
Estimated Fair Value
Due after ten years	133,656
Fair values of available-for-sale investment securities pledged	$ 640,900	$ 767,400