SEGMENT INFORMATION (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Information about reportable segments
Net interest income	$ 111,030	$ 94,872
Provision for credit losses	3,500	906
Noninterest revenues	13,495	65,673
Loss on sales of investment securities	(52,329)	0
Gain on debt extinguishment	242	0
Other noninterest revenues	65,582
Amortization of intangible assets	3,667	3,732
Acquisition expenses	57	299
Other operating expenses	110,328	95,776
Income before income taxes	6,973	59,832
Assets	15,255,953	15,625,883	$ 15,835,651
Goodwill	842,936	799,080	$ 841,841
Core deposit intangibles & Other intangibles	57,978	63,958
Eliminations
Information about reportable segments
Net interest income	0	0
Provision for credit losses	0	0
Noninterest revenues		(2,063)
Loss on sales of investment securities	0
Gain on debt extinguishment	0
Other noninterest revenues	(2,229)
Amortization of intangible assets	0	0
Acquisition expenses	0	0
Other operating expenses	(2,229)	(2,063)
Income before income taxes	0	0
Assets	(111,770)	(134,446)
Goodwill	0	0
Core deposit intangibles & Other intangibles	0	0
Banking | Operating Segments
Information about reportable segments
Net interest income	110,682	94,798
Provision for credit losses	3,500	906
Noninterest revenues		18,008
Loss on sales of investment securities	(52,329)
Gain on debt extinguishment	242
Other noninterest revenues	17,362
Amortization of intangible assets	1,206	1,045
Acquisition expenses	17	298
Other operating expenses	78,266	66,656
Income before income taxes	(7,032)	43,901
Assets	15,040,487	15,402,218
Goodwill	733,064	689,868
Core deposit intangibles & Other intangibles	11,629	8,041
Employee Benefit Services | Operating Segments
Information about reportable segments
Net interest income	254	68
Provision for credit losses	0	0
Noninterest revenues		30,188
Loss on sales of investment securities	0
Gain on debt extinguishment	0
Other noninterest revenues	30,221
Amortization of intangible assets	1,633	1,671
Acquisition expenses	0	1
Other operating expenses	18,964	17,597
Income before income taxes	9,878	10,987
Assets	229,091	260,166
Goodwill	85,384	85,292
Core deposit intangibles & Other intangibles	31,778	38,348
All Other | Operating Segments
Information about reportable segments
Net interest income	94	6
Provision for credit losses	0	0
Noninterest revenues		19,540
Loss on sales of investment securities	0
Gain on debt extinguishment	0
Other noninterest revenues	20,228
Amortization of intangible assets	828	1,016
Acquisition expenses	40	0
Other operating expenses	15,327	13,586
Income before income taxes	4,127	4,944
Assets	98,145	97,945
Goodwill	24,488	23,920
Core deposit intangibles & Other intangibles	$ 14,571	$ 17,569