INVESTMENT SECURITIES - Schedule of Investment Securities' Gross Unrealized Losses and Fair Value by Investment Category (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Available-for-sale debt securities:
Available-for-sale debt securities, Less than 12 months, Fair value	$ 20,220	$ 1,530,406
Available-for-sale debt securities, Less than 12 months, Unrealized loss	1,121	171,140
Available-for-sale debt securities, 12 months or longer, Fair value	3,671,321	2,562,615
Available-for-sale debt securities, 12 months or longer, Unrealized loss	891,528	570,350
Available-for-sale debt securities, Total, Fair value	3,691,541	4,093,021
Available-for-sale debt securities, Total, Unrealized loss	892,649	741,490
CMO
Available-for-sale debt securities:
Available-for-sale debt securities, Less than 12 months, Fair value	0	158,449
Available-for-sale debt securities, Less than 12 months, Unrealized loss	0	13,855
Available-for-sale debt securities, 12 months or longer, Fair value	454,664	347,931
Available-for-sale debt securities, 12 months or longer, Unrealized loss	118,729	88,599
Available-for-sale debt securities, Total, Fair value	454,664	506,380
Available-for-sale debt securities, Total, Unrealized loss	118,729	102,454
FNMA MBS
Available-for-sale debt securities:
Available-for-sale debt securities, Less than 12 months, Fair value	8,792	1,237,560
Available-for-sale debt securities, Less than 12 months, Unrealized loss	467	145,752
Available-for-sale debt securities, 12 months or longer, Fair value	2,904,620	2,012,698
Available-for-sale debt securities, 12 months or longer, Unrealized loss	694,216	427,026
Available-for-sale debt securities, Total, Fair value	2,913,412	3,250,258
Available-for-sale debt securities, Total, Unrealized loss	694,683	572,778
FHLMC MBS
Available-for-sale debt securities:
Available-for-sale debt securities, Less than 12 months, Fair value	7	102,321
Available-for-sale debt securities, Less than 12 months, Unrealized loss	0	9,268
Available-for-sale debt securities, 12 months or longer, Fair value	110,712	19,671
Available-for-sale debt securities, 12 months or longer, Unrealized loss	18,280	4,287
Available-for-sale debt securities, Total, Fair value	110,719	121,992
Available-for-sale debt securities, Total, Unrealized loss	18,280	13,555
GNMA MBS
Available-for-sale debt securities:
Available-for-sale debt securities, Less than 12 months, Fair value	11,421	32,076
Available-for-sale debt securities, Less than 12 months, Unrealized loss	654	2,265
Available-for-sale debt securities, 12 months or longer, Fair value	31,330	4,030
Available-for-sale debt securities, 12 months or longer, Unrealized loss	4,216	713
Available-for-sale debt securities, Total, Fair value	42,751	36,106
Available-for-sale debt securities, Total, Unrealized loss	4,870	2,978
GSE agency notes
Available-for-sale debt securities:
Available-for-sale debt securities, Less than 12 months, Fair value	0	0
Available-for-sale debt securities, Less than 12 months, Unrealized loss	0	0
Available-for-sale debt securities, 12 months or longer, Fair value	169,995	178,285
Available-for-sale debt securities, 12 months or longer, Unrealized loss	56,087	49,725
Available-for-sale debt securities, Total, Fair value	169,995	178,285
Available-for-sale debt securities, Total, Unrealized loss	$ 56,087	$ 49,725

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