Securities (Details 5) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Amortized Cost
Due within one year	$ 638,257
Due after one year through five years	629,892
Due after five years through ten years	176,117
Due after ten years	1,548,497
Total available-for-sale investment securities	2,992,763
Estimated Fair Value
Due within one year	621,343
Due after one year through five years	623,058
Due after five years through ten years	172,902
Due after ten years	1,539,473
Total available-for-sale investment securities	2,956,776	$ 3,335,795
Fair values of available-for-sale investment securities pledged	$ 584,900	$ 767,400