Investment Securities - Maturities of Investment Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Held-to-maturity, amortized cost, one year or less	$ 4,543
Held-to-maturity, amortized cost, after one through five years	15,414
Held-to-maturity, amortized cost, after five through ten years	7,299
Held-to-maturity, amortized cost, after ten years	0
Held-to-maturity, amortized cost, securities not due on a single maturity date	27,121
Amortized Cost	54,377	$ 40,927
Held-to-maturity, fair value, one year or less	4,563
Held-to-maturity, fair value, after one through five years	15,769
Held-to-maturity, fair value, after five through ten years	7,594
Held-to-maturity, fair value, after ten years	0
Held-to-maturity, fair value, securities not due on a single maturity date	27,788
Held-to-maturity, fair value, total	55,714	41,855
Available-for-sale, amortized cost, one year or less	437,199
Available-for-sale, amortized cost, after one through five years	34,541
Available-for-sale, amortized cost, after five through ten years	108,605
Available-for-sale, amortized cost, after ten years	686,714
Available-for-sale, amortized cost, securities not due on a single maturity date	1,150,878
Available-for-sale, amortized cost, other securities (no maturity)	561
Amortized Cost	2,418,498	3,263,151
Available-for-sale, fair value, one year or less	437,187
Available-for-sale, fair value, after one through five years	34,889
Available-for-sale, fair value, after five through ten years	109,611
Available-for-sale, fair value, after ten years	703,839
Available-for-sale, fair value, securities not due on a single maturity date	1,179,837
Available-for-sale, fair value, other securities (no maturity)	1,277
Available-for-sale, fair value, total	$ 2,466,640	$ 3,288,343