SEGMENT REPORTING - Operating Segments and Reconciliation of Information to Condensed Consolidated Financial Statements (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Segment Reporting Information [Line Items]
Interest income	$ 130,422	$ 111,129	$ 350,367	$ 340,213
Interest expense	17,462	4,525	30,006	20,963
Provision/ (credit) for credit losses	18,890	(8,229)	23,571	(47,141)
Non-interest income	16,882	24,394	72,722	79,519
Non-interest expense	65,780	63,181	192,918	194,329
Income before income tax expense	45,172	76,046	176,594	251,581
Income tax expense	11,588	19,070	44,275	61,878
Net income	33,584	56,976	132,319	189,703
Assets	13,765,597	13,017,464	13,765,597	13,017,464	$ 12,590,726
Inter-Segment Elimination
Segment Reporting Information [Line Items]
Interest income	(26)	(3)	(32)	(9)
Interest expense	(26)	(3)	(32)	(9)
Provision/ (credit) for credit losses	0	0	0	0
Non-interest income	(305)	(217)	(15,095)	(4,651)
Non-interest expense	(139)	(217)	(579)	(651)
Income before income tax expense	(166)	0	(14,516)	(4,000)
Income tax expense	0	0	0	0
Net income	(166)	0	(14,516)	(4,000)
Assets	(88,324)	(66,527)	(88,324)	(66,527)
Community Banking | Operating Segments
Segment Reporting Information [Line Items]
Interest income	130,422	111,129	350,367	340,213
Interest expense	17,488	4,528	30,038	20,972
Provision/ (credit) for credit losses	18,890	(8,229)	23,571	(47,141)
Non-interest income	11,956	16,644	51,669	62,083
Non-interest expense	61,135	58,059	177,637	179,803
Income before income tax expense	44,865	73,415	170,790	248,662
Income tax expense	11,281	18,385	38,471	59,951
Net income	33,584	55,030	132,319	188,711
Assets	13,783,402	13,017,464	13,783,402	13,017,464
Insurance | Operating Segments
Segment Reporting Information [Line Items]
Interest income	23	0	24	2
Interest expense	0	0	0	0
Provision/ (credit) for credit losses	0	0	0	0
Non-interest income	(184)	2,282	19,449	5,679
Non-interest expense	(107)	1,696	3,756	4,507
Income before income tax expense	(54)	586	15,717	1,174
Income tax expense	53	185	4,450	347
Net income	(107)	401	11,267	827
Assets	17,698	9,203	17,698	9,203
Investment Management | Operating Segments
Segment Reporting Information [Line Items]
Interest income	3	3	8	7
Interest expense	0	0	0	0
Provision/ (credit) for credit losses	0	0	0	0
Non-interest income	5,415	5,685	16,699	16,408
Non-interest expense	4,891	3,643	12,104	10,670
Income before income tax expense	527	2,045	4,603	5,745
Income tax expense	254	500	1,354	1,580
Net income	273	1,545	3,249	4,165
Assets	$ 52,821	$ 57,324	$ 52,821	$ 57,324