SEGMENT INFORMATION (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Information about reportable segments
Net interest income	$ 109,279	$ 103,141	$ 220,309	$ 198,013
Provision for credit losses	752	6,038	4,252	6,944
Noninterest revenues	65,984	64,097	79,479	129,770
Loss on sales of investment securities	0	0	(52,329)	0
Gain on debt extinguishment	0	0	242	0
Other noninterest revenues			131,566
Amortization of intangible assets	3,705	3,851	7,372	7,583
Acquisition expenses	(1)	3,960	56	4,259
Acquisition-related contingent consideration adjustment	1,000	400	1,000	400
Other operating expenses	108,334	102,213	218,662	197,989
Income before income taxes	61,473	50,776	68,446	110,608
Assets	15,108,050	15,487,833	15,108,050	15,487,833	$ 15,835,651
Goodwill	843,960	849,813	843,960	849,813	$ 841,841
Core deposit intangibles & Other intangibles	57,749	68,078	57,749	68,078
Eliminations
Information about reportable segments
Net interest income	0	0	0	0
Provision for credit losses	0	0	0	0
Noninterest revenues	(2,119)	(1,871)		(3,934)
Loss on sales of investment securities			0
Gain on debt extinguishment			0
Other noninterest revenues			(4,348)
Amortization of intangible assets	0	0	0	0
Acquisition expenses	0	0	0	0
Acquisition-related contingent consideration adjustment	0	0	0	0
Other operating expenses	(2,119)	(1,871)	(4,348)	(3,934)
Income before income taxes	0	0	0	0
Assets	(115,416)	(121,326)	(115,416)	(121,326)
Goodwill	0	0	0	0
Core deposit intangibles & Other intangibles	0	0	0	0
Banking | Operating Segments
Information about reportable segments
Net interest income	108,770	103,068	219,452	197,866
Provision for credit losses	752	6,038	4,252	6,944
Noninterest revenues	18,587	18,199		36,207
Loss on sales of investment securities			(52,329)
Gain on debt extinguishment			242
Other noninterest revenues			35,949
Amortization of intangible assets	1,160	1,195	2,366	2,240
Acquisition expenses	(1)	3,958	16	4,256
Acquisition-related contingent consideration adjustment	0	0	0	0
Other operating expenses	75,497	72,406	153,763	139,062
Income before income taxes	49,949	37,670	42,917	81,571
Assets	14,885,490	15,267,283	14,885,490	15,267,283
Goodwill	732,598	740,601	732,598	740,601
Core deposit intangibles & Other intangibles	11,114	14,817	11,114	14,817
Employee Benefit Services | Operating Segments
Information about reportable segments
Net interest income	389	67	643	135
Provision for credit losses	0	0	0	0
Noninterest revenues	29,418	29,454		59,642
Loss on sales of investment securities			0
Gain on debt extinguishment			0
Other noninterest revenues			59,639
Amortization of intangible assets	1,631	1,670	3,264	3,341
Acquisition expenses	0	2	0	3
Acquisition-related contingent consideration adjustment	(100)	(100)	(100)	(100)
Other operating expenses	18,749	17,718	37,713	35,315
Income before income taxes	9,527	10,231	19,405	21,218
Assets	235,655	243,309	235,655	243,309
Goodwill	85,384	85,289	85,384	85,289
Core deposit intangibles & Other intangibles	30,147	36,679	30,147	36,679
All Other | Operating Segments
Information about reportable segments
Net interest income	120	6	214	12
Provision for credit losses	0	0	0	0
Noninterest revenues	20,098	18,315		37,855
Loss on sales of investment securities			0
Gain on debt extinguishment			0
Other noninterest revenues			40,326
Amortization of intangible assets	914	986	1,742	2,002
Acquisition expenses	0	0	40	0
Acquisition-related contingent consideration adjustment	1,100	500	1,100	500
Other operating expenses	16,207	13,960	31,534	27,546
Income before income taxes	1,997	2,875	6,124	7,819
Assets	102,321	98,567	102,321	98,567
Goodwill	25,978	23,923	25,978	23,923
Core deposit intangibles & Other intangibles	$ 16,488	$ 16,582	$ 16,488	$ 16,582