Securities - Remaining Contractual Maturity of Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Available-for-sale Securities, Amortized Cost [Abstract]
One year or less	$ 326,292
After one year to five years	178,785
After five years to ten years	490,875
After ten years	0
Securities that do not have a single contractual maturity date	2,303,457
Amortized Cost	3,299,409	$ 2,851,479
Fair Value
One year or less	326,171
After one year to five years	178,718
After five years to ten years	490,693
After ten years	0
Securities that do not have a single contractual maturity date	2,387,283
Fair Value	3,382,865	$ 2,873,386
Held-to-maturity Securities, Amortized Cost [Abstract]
One year or less	8,111
After one year to five years	5,573
After five years to ten years	3,349
After ten years	2,792
Securities that do not have a single contractual maturity date	0
Amortized Cost	19,825
Held-to-maturity Securities, Fair Value [Abstract]
One year or less	8,118
After one year to five years	5,578
After five years to ten years	3,352
After ten years	2,794
Securities that do not have a single contractual maturity date	0
Fair Value	$ 19,842