INVESTMENTS - Age of Gross Unrealized Losses and Associated Fair Value by Investment Category (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months Fair Value	$ 2,338,934	$ 1,970,822
Less than 12 Months Unrealized Loss	(205,578)	(27,427)
12 Months or More Fair Value	1,143,228	171,838
12 Months or More Unrealized Loss	(229,962)	(4,187)
Total Fair Value	3,482,162	2,142,660
Total Unrealized Loss	(435,540)	(31,614)
Amortized Cost	85,823	98,420
Debt Securities, Held-to-maturity, Fair Value	78,924	99,898
Debt Securities, Available-for-sale, Amortized Cost	3,959,270	4,180,589
Investment securities available-for-sale, at fair value (amortized cost $3,959,270 at September 30, 2022 and $4,180,589 at December 31, 2021)	3,531,353	4,207,846
U.S. Treasuries
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months Fair Value	13,018	24,755
Less than 12 Months Unrealized Loss	(1,343)	(190)
12 Months or More Fair Value	21,384	0
12 Months or More Unrealized Loss	(3,568)	0
Total Fair Value	34,402	24,755
Total Unrealized Loss	(4,911)	(190)
Amortized Cost	0	0
Debt Securities, Held-to-maturity, Fair Value	0	0
Debt Securities, Available-for-sale, Amortized Cost	39,313	34,961
Investment securities available-for-sale, at fair value (amortized cost $3,959,270 at September 30, 2022 and $4,180,589 at December 31, 2021)	34,402	34,776
Securities of U.S. government agencies and corporations
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months Fair Value	66,309	17,382
Less than 12 Months Unrealized Loss	(13,723)	(128)
12 Months or More Fair Value	0	0
12 Months or More Unrealized Loss	0	0
Total Fair Value	66,309	17,382
Total Unrealized Loss	(13,723)	(128)
Amortized Cost	0	0
Debt Securities, Held-to-maturity, Fair Value	0	0
Debt Securities, Available-for-sale, Amortized Cost	80,032	78,998
Investment securities available-for-sale, at fair value (amortized cost $3,959,270 at September 30, 2022 and $4,180,589 at December 31, 2021)	66,309	79,117
Residential Mortgage Backed Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months Fair Value	208,158	459,098
Less than 12 Months Unrealized Loss	(26,128)	(8,375)
12 Months or More Fair Value	367,289	78,090
12 Months or More Unrealized Loss	(76,093)	(2,173)
Total Fair Value	575,447	537,188
Total Unrealized Loss	(102,221)	(10,548)
Amortized Cost	0	0
Debt Securities, Held-to-maturity, Fair Value	0	0
Debt Securities, Available-for-sale, Amortized Cost	688,513	728,050
Investment securities available-for-sale, at fair value (amortized cost $3,959,270 at September 30, 2022 and $4,180,589 at December 31, 2021)	586,292	724,137
Commercial Mortgage Backed Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months Fair Value	613,089	205,520
Less than 12 Months Unrealized Loss	(32,931)	(2,149)
12 Months or More Fair Value	99,521	13,818
12 Months or More Unrealized Loss	(17,792)	(203)
Total Fair Value	712,610	219,338
Total Unrealized Loss	(50,723)	(2,352)
Amortized Cost	36,714	46,362
Debt Securities, Held-to-maturity, Fair Value	32,956	47,013
Debt Securities, Available-for-sale, Amortized Cost	731,619	729,948
Investment securities available-for-sale, at fair value (amortized cost $3,959,270 at September 30, 2022 and $4,180,589 at December 31, 2021)	684,654	731,890
Collateralized Mortgage Backed Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months Fair Value	269,501	369,318
Less than 12 Months Unrealized Loss	(18,727)	(6,110)
12 Months or More Fair Value	228,192	12,485
12 Months or More Unrealized Loss	(42,536)	(387)
Total Fair Value	497,693	381,803
Total Unrealized Loss	(61,263)	(6,497)
Amortized Cost	9,692	11,882
Debt Securities, Held-to-maturity, Fair Value	8,900	12,103
Debt Securities, Available-for-sale, Amortized Cost	550,209	696,258
Investment securities available-for-sale, at fair value (amortized cost $3,959,270 at September 30, 2022 and $4,180,589 at December 31, 2021)	489,848	697,740
Obligations of state and other political subdivisions
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months Fair Value	492,728	380,735
Less than 12 Months Unrealized Loss	(69,208)	(7,543)
12 Months or More Fair Value	271,666	55,568
12 Months or More Unrealized Loss	(70,075)	(1,051)
Total Fair Value	764,394	436,303
Total Unrealized Loss	(139,283)	(8,594)
Amortized Cost	8,167	8,926
Debt Securities, Held-to-maturity, Fair Value	7,872	9,841
Debt Securities, Available-for-sale, Amortized Cost	971,655	1,058,735
Investment securities available-for-sale, at fair value (amortized cost $3,959,270 at September 30, 2022 and $4,180,589 at December 31, 2021)	833,099	1,085,732
Asset-backed Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months Fair Value	558,218	482,118
Less than 12 Months Unrealized Loss	(37,812)	(2,578)
12 Months or More Fair Value	128,087	0
12 Months or More Unrealized Loss	(17,487)	0
Total Fair Value	686,305	482,118
Total Unrealized Loss	(55,299)	(2,578)
Amortized Cost	0	0
Debt Securities, Held-to-maturity, Fair Value	0	0
Debt Securities, Available-for-sale, Amortized Cost	760,915	720,638
Investment securities available-for-sale, at fair value (amortized cost $3,959,270 at September 30, 2022 and $4,180,589 at December 31, 2021)	705,773	719,581
Other securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months Fair Value	117,913	31,896
Less than 12 Months Unrealized Loss	(5,706)	(354)
12 Months or More Fair Value	27,089	11,877
12 Months or More Unrealized Loss	(2,411)	(373)
Total Fair Value	145,002	43,773
Total Unrealized Loss	(8,117)	(727)
Amortized Cost	31,250	31,250
Debt Securities, Held-to-maturity, Fair Value	29,196	30,941
Debt Securities, Available-for-sale, Amortized Cost	137,014	133,001
Investment securities available-for-sale, at fair value (amortized cost $3,959,270 at September 30, 2022 and $4,180,589 at December 31, 2021)	$ 130,976	$ 134,873