Investments (Aggregate Values and Unrealized Gains and Losses) (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Investment securities available for sale
Investment securities available for sale, cost	$ 9,215,219	$ 6,911,965
Investment securities available for sale, gross unrealized gains	45,006	111,189
Investment securities available for sale, gross unrealized losses	56,798	8,911
Investment securities available for sale, fair value	9,203,427	7,014,243
Investments in ME securities, cost	72,894	84,837
Investment in marketable equity securities, gross unrealized gains	24,879	8,654
Investment in marketable equity securities, gross unrealized losses	245	1,811
Investment in marketable equity securities, fair value	97,528	91,680
Investment securities held to maturity
Investment securities held to maturity, cost	3,809,453	2,816,982
Investment securities held to maturity, gross unrealied gains	5,722	21,573
Investment securities held to maturity, gross unrealized losses	55,525	56
Investment securities held to maturity, fair value	3,759,650	2,838,499
Total investment securities, cost	13,097,566	9,813,784
Total investment securities, gross unrealized gains	75,607	141,416
Total investment securities, fair value	112,568	10,778
Total investment securities, gross unrealized losses	13,060,605	9,944,422
U. S. Treasury
Investment securities available for sale
Investment securities available for sale, cost	2,006,788	499,832
Investment securities available for sale, gross unrealized gains	106	101
Investment securities available for sale, gross unrealized losses	1,924	0
Investment securities available for sale, fair value	2,004,970	499,933
Government Agency
Investment securities available for sale
Investment securities available for sale, cost	797,725	706,241
Investment securities available for sale, gross unrealized gains	4,659	723
Investment securities available for sale, gross unrealized losses	3,624	5,573
Investment securities available for sale, fair value	798,760	701,391
Residential Mortgage Backed Securities
Investment securities available for sale
Investment securities available for sale, cost	4,756,977	4,369,130
Investment securities available for sale, gross unrealized gains	8,229	70,283
Investment securities available for sale, gross unrealized losses	36,793	1,310
Investment securities available for sale, fair value	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, gross unrealied gains	5,690	17,689
Investment securities held to maturity, gross unrealized losses	21,957	0
Investment securities held to maturity, fair value	2,306,262	1,895,381
Commercial Mortgage Backed Securities
Investment securities available for sale
Investment securities available for sale, cost	1,071,309	745,892
Investment securities available for sale, gross unrealized gains	5,364	25,645
Investment securities available for sale, gross unrealized losses	13,924	0
Investment securities available for sale, fair value	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, gross unrealied gains	32	3,884
Investment securities held to maturity, gross unrealized losses	33,568	56
Investment securities held to maturity, fair value	1,451,380	940,862
Corporate Bonds
Investment securities available for sale
Investment securities available for sale, cost	582,420	590,870
Investment securities available for sale, gross unrealized gains	26,648	14,437
Investment securities available for sale, gross unrealized losses	533	2,028
Investment securities available for sale, fair value	608,535	603,279
Other Debt Obligations
Investment securities held to maturity
Investment securities held to maturity, cost	2,008	2,256
Investment securities held to maturity, gross unrealied gains	0	0
Investment securities held to maturity, gross unrealized losses	0	0
Investment securities held to maturity, fair value	$ 2,008	$ 2,256

Debt Securities, Available-for-sale, Held-to-maturity and Equity Securities

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