Investments (Unrealized Losses) (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Investment securities available for sale:
Less than 12 months, fair value	$ 6,725,062	$ 760,153
Less than 12 months, unrealized losses	54,666	6,466
Longer than 12 months, fair value	191,286	351,841
Longer than 12 months, unrealized losses	2,132	2,445
Total fair value	6,916,348	1,111,994
Total unrealized losses	56,798	8,911
U. S. Treasury
Investment securities available for sale:
Less than 12 months, fair value	1,810,924
Less than 12 months, unrealized losses	1,924
Longer than 12 months, fair value	0
Longer than 12 months, unrealized losses	0
Total fair value	1,810,924
Total unrealized losses	1,924
Government Agency
Investment securities available for sale:
Less than 12 months, fair value	222,401	268,622
Less than 12 months, unrealized losses	1,516	3,197
Longer than 12 months, fair value	189,935	328,777
Longer than 12 months, unrealized losses	2,108	2,376
Total fair value	412,336	597,399
Total unrealized losses	3,624	5,573
Residential Mortgage Backed Securities
Investment securities available for sale:
Less than 12 months, fair value	3,992,305	433,816
Less than 12 months, unrealized losses	36,769	1,241
Longer than 12 months, fair value	1,351	23,064
Longer than 12 months, unrealized losses	24	69
Total fair value	3,993,656	456,880
Total unrealized losses	36,793	1,310
Commercial Mortgage Backed Securities
Investment securities available for sale:
Less than 12 months, fair value	647,101
Less than 12 months, unrealized losses	13,924
Longer than 12 months, fair value	0
Longer than 12 months, unrealized losses	0
Total fair value	647,101
Total unrealized losses	13,924
Corporate Bonds
Investment securities available for sale:
Less than 12 months, fair value	52,331	57,715
Less than 12 months, unrealized losses	533	2,028
Longer than 12 months, fair value	0	0
Longer than 12 months, unrealized losses	0	0
Total fair value	52,331	57,715
Total unrealized losses	$ 533	$ 2,028

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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