Securities - Remaining Contractual Maturity of Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Available-for-sale Securities, Amortized Cost [Abstract]
One year or less	$ 270,623
After one year to five years	185,159
After five years to ten years	578,516
After ten years	0
Securities that do not have a single contractual maturity date	2,319,827
Amortized Cost	3,354,125	$ 2,851,479
Fair Value
One year or less	274,363
After one year to five years	187,718
After five years to ten years	586,512
After ten years	0
Securities that do not have a single contractual maturity date	2,387,269
Fair Value	3,435,862	$ 2,873,386
Held-to-maturity Securities, Amortized Cost [Abstract]
One year or less	8,070
After one year to five years	5,452
After five years to ten years	3,315
After ten years	2,791
Securities that do not have a single contractual maturity date	0
Amortized Cost	19,628
Held-to-maturity Securities, Fair Value [Abstract]
One year or less	8,089
After one year to five years	5,465
After five years to ten years	3,323
After ten years	2,799
Securities that do not have a single contractual maturity date	0
Fair Value	$ 19,676