Investment Securities (Contractual Maturities of Investment Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Amortized Cost
Due in one year or less	$ 183,996	$ 82,206
Due in one to five years	62,679	168,855
Due in five to ten years	186,683	121,129
Due after ten years	292,308	128,339
Amortized Cost	3,086,824	2,185,494
Fair Value
Due in one year or less	185,035	82,153
Due in one to five years	64,064	169,307
Due in five to ten years	184,666	115,206
Due after ten years	292,924	129,580
Fair Value	3,106,214	2,126,081
Amortized Cost
Due in one year or less	6,061	10,009
Due in one to five years	28,697	29,436
Due in five to ten years	213,104	295,897
Due after ten years	886,538	732,097
Amortized Cost	1,134,400	1,067,439
Fair Value
Due in one year or less	6,074	9,979
Due in one to five years	28,986	28,995
Due in five to ten years	216,957	290,206
Due after ten years	886,379	706,916
Fair Value	1,138,396	1,036,096
Mortgage-backed
Amortized Cost
Mortgage-backed	2,361,158	1,684,965
Fair Value
Mortgage-backed	$ 2,379,525	$ 1,629,835