Securities, HTM Debt Securities, Contractual Maturities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Held-to-maturity Securities, Debt Maturities, Amortized Cost [Abstract]
Within one year	$ 89,011
From one to five years	53,217
From five to ten years	215,931
After ten years	301,790
Amortized cost	659,949	$ 484,073
Held-to-maturity Securities, Debt Maturities, Estimated Fair Value [Abstract]
Within one year	89,011
From one to five years	53,177
From five to ten years	209,974
After ten years	293,570
Fair value	$ 645,732	$ 481,871