Securities - Schedule of Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Amortized Cost
Within one year	$ 202
Over one to five years	1,333
Over five to ten years	36,822
Over ten years	230,405
Total securities	268,762
Estimated Fair Value
Within one year	204
Over one to five years	1,329
Over five to ten years	35,912
Over ten years	228,454
Total securities	265,899
Amortized Cost
Within one year	34,977
Over one to five years	17,522
Over five to ten years	406,424
Over ten years	2,310,453
Total held-to-maturity securities	2,769,376	$ 2,740,132
Estimated Fair Value
Within one year	34,979
Over one to five years	17,541
Over five to ten years	389,288
Over ten years	2,279,915
Total securities	$ 2,721,723	$ 2,690,546