Investments (Maturity Information) (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Investment securities available for sale
Total investment securities available for sale, cost	$ 9,215,219	$ 6,911,965
Investment securities available for sale	9,203,427	7,014,243
Investment securities held to maturity
Maturing in one year or less, cost	2,008	1,507
Maturing in one year or less, fair value	2,008	1,507
Maturing in one through five years, cost	0	749
Maturing in one through five years, fair value	0	749
Investment securities held to maturity, cost	3,809,453	2,816,982
Total investment securities held to maturity, fair value	3,759,650	2,838,499
Debt Securities
Investment securities available for sale
Maturing in one year or less, cost	200	500,846
Maturing in one through five years, cost	2,049,068	72,565
Maturing in five through ten years, cost	523,290	508,320
Maturing in over ten years, cost	16,650	8,971
Maturing in one year or less, fair value	202	500,954
Maturing in one through five years, fair value	2,048,259	73,881
Maturing in five through ten years, fair value	547,912	519,570
Maturing in over ten years, fair value	17,132	8,807
Government Agency
Investment securities available for sale
Total investment securities available for sale, cost	797,725	706,241
Investment securities available for sale	798,760	701,391
Residential Mortgage Backed Securities
Investment securities available for sale
Total investment securities available for sale, cost	4,756,977	4,369,130
Investment securities available for sale	4,728,413	4,438,103
Investment securities held to maturity
Investment securities held to maturity, cost	2,322,529	1,877,692
Investment securities held to maturity, fair value	2,306,262	1,895,381
Total investment securities held to maturity, fair value	2,306,262	1,895,381
Commercial Mortgage Backed Securities
Investment securities available for sale
Total investment securities available for sale, cost	1,071,309	745,892
Investment securities available for sale	1,062,749	771,537
Investment securities held to maturity
Investment securities held to maturity, cost	1,484,916	937,034
Investment securities held to maturity, fair value	1,451,380	940,862
Total investment securities held to maturity, fair value	$ 1,451,380	$ 940,862