INVESTMENT SECURITIES - Unrealized Loss Position (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Unrealized loss position for less than 12 months
Unrealized loss position for less than 12 months, fair value	$ 2,436,978	$ 3,012,189
Unrealized loss position for less than 12 months, unrealized loss	(23,476)	(35,366)
Unrealized loss position for more than 12 months
Unrealized loss position for more than 12 months, fair value	5,226,775	5,699,370
Unrealized loss position for more than 12 months, unrealized loss	(281,040)	(453,699)
Auction-rate certificates backed by Government guaranteed student loans
Unrealized loss position for less than 12 months
Unrealized loss position for less than 12 months, fair value		0
Unrealized loss position for less than 12 months, unrealized loss		0
Unrealized loss position for more than 12 months
Unrealized loss position for more than 12 months, fair value		19,476
Unrealized loss position for more than 12 months, unrealized loss		(197)
Government/GSE guaranteed mortgage-backed securities
Unrealized loss position for less than 12 months
Unrealized loss position for less than 12 months, fair value	799,619	1,269,655
Unrealized loss position for less than 12 months, unrealized loss	(4,695)	(18,102)
Unrealized loss position for more than 12 months
Unrealized loss position for more than 12 months, fair value	2,008,388	1,971,526
Unrealized loss position for more than 12 months, unrealized loss	(84,539)	(138,598)
U.S. Treasuries
Unrealized loss position for less than 12 months
Unrealized loss position for less than 12 months, fair value	29,902	590,307
Unrealized loss position for less than 12 months, unrealized loss	(13)	(4,375)
Unrealized loss position for more than 12 months
Unrealized loss position for more than 12 months, fair value	95,270	58,523
Unrealized loss position for more than 12 months, unrealized loss	(35)	(317)
AgVantage
Unrealized loss position for less than 12 months
Unrealized loss position for less than 12 months, fair value	1,607,457	1,152,227
Unrealized loss position for less than 12 months, unrealized loss	(18,768)	(12,889)
Unrealized loss position for more than 12 months
Unrealized loss position for more than 12 months, fair value	3,123,117	3,649,845
Unrealized loss position for more than 12 months, unrealized loss	$ (196,466)	$ (314,587)