Securities - Remaining Contractual Maturity of Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Available-for-Sale Securities, Amortized Cost Basis [Abstract]
One year or less	$ 113,548
After one year to five years	176,349
After five years to ten years	207,827
After ten years	0
Securities that do not have a single contractual maturity date	1,814,196
Amortized Cost	2,311,920
Available-for-Sale Securities, Fair Value [Abstract]
One year or less	111,755
After one year to five years	173,565
After five years to ten years	204,546
After ten years	0
Securities that do not have a single contractual maturity date	1,782,143
Total	2,272,009
Held-to-Maturity Securities, Amortized Cost [Abstract]
One year or less	7,580
After one year to five years	2,236
After five years to ten years	360
After ten years	0
Securities that do not have a single contractual maturity date	0
Amortized Cost	10,176	$ 13,760
Held-to-Maturity Securities, Fair Value [Abstract]
One year or less	7,353
After one year to five years	2,169
After five years to ten years	349
After ten years	0
Securities that do not have a single contractual maturity date	0
Total	$ 9,871	$ 12,013