Securities (Details 5) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Amortized Cost
Due within one year	$ 482,138
Due after one year through five years	804,701
Due after five years through ten years	185,889
Due after ten years	1,382,696
Total available-for-sale investment securities	2,855,424
Estimated Fair Value
Due within one year	469,865
Due after one year through five years	794,668
Due after five years through ten years	182,964
Due after ten years	1,375,228
Total available-for-sale investment securities	2,822,725	$ 3,335,795
Amortized Cost
Due after ten years	121,131
Estimated Fair Value
Due after ten years	121,803
Fair values of available-for-sale investment securities pledged	$ 577,500	$ 767,400