Investment Securities - Maturities of Investment Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Held-to-maturity, amortized cost, one year or less	$ 4,928
Held-to-maturity, amortized cost, after one through five years	15,201
Held-to-maturity, amortized cost, after five through ten years	5,918
Held-to-maturity, amortized cost, after ten years	0
Held-to-maturity, amortized cost, securities not due on a single maturity date	25,980
Amortized Cost	52,027	$ 40,927
Held-to-maturity, fair value, one year or less	4,962
Held-to-maturity, fair value, after one through five years	15,793
Held-to-maturity, fair value, after five through ten years	6,219
Held-to-maturity, fair value, after ten years	0
Held-to-maturity, fair value, securities not due on a single maturity date	26,777
Held-to-maturity, fair value, total	53,751	41,855
Available-for-sale, amortized cost, one year or less	15,006
Available-for-sale, amortized cost, after one through five years	35,995
Available-for-sale, amortized cost, after five through ten years	203,777
Available-for-sale, amortized cost, after ten years	1,047,772
Available-for-sale, amortized cost, securities not due on a single maturity date	1,125,484
Available-for-sale, amortized cost, other securities (no maturity)	514
Amortized Cost	2,428,548	3,263,151
Available-for-sale, fair value, one year or less	15,077
Available-for-sale, fair value, after one through five years	36,348
Available-for-sale, fair value, after five through ten years	205,627
Available-for-sale, fair value, after ten years	1,084,495
Available-for-sale, fair value, securities not due on a single maturity date	1,154,086
Available-for-sale, fair value, other securities (no maturity)	1,263
Available-for-sale, fair value, total	$ 2,496,896	$ 3,288,343