SEGMENT INFORMATION - Reportable segments information (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2024	Mar. 31, 2023
Reconciliation of operating profit loss from segment to consolidated
Operating income before income taxes	$ 53,043	$ 6,973
Unrealized (loss) gain on equity securities	16	0
Amortization of intangible assets	3,576	3,667
Merger and acquisition integration related (recoveries) expenses	35	57
Litigation accrual	119	0
Operating Segment
Reconciliation of operating profit loss from segment to consolidated
Operating income before income taxes	56,757	62,784
Banking and Corporate \| Operating Segment
Reconciliation of operating profit loss from segment to consolidated
Operating income before income taxes	40,024	45,214
Unrealized (loss) gain on equity securities	16
Amortization of intangible assets	973	1,206
Merger and acquisition integration related (recoveries) expenses	0	17
Litigation accrual	0
Employee Benefit Services \| Operating Segment
Reconciliation of operating profit loss from segment to consolidated
Operating income before income taxes	12,860	12,167
Unrealized (loss) gain on equity securities	0
Amortization of intangible assets	1,725	1,633
Merger and acquisition integration related (recoveries) expenses	35	0
Litigation accrual	0
Insurance \| Operating Segment
Reconciliation of operating profit loss from segment to consolidated
Operating income before income taxes	1,031	2,802
Unrealized (loss) gain on equity securities	0
Amortization of intangible assets	673	630
Merger and acquisition integration related (recoveries) expenses	0	40
Litigation accrual	119
Wealth Management \| Operating Segment
Reconciliation of operating profit loss from segment to consolidated
Operating income before income taxes	2,842	2,601
Unrealized (loss) gain on equity securities	0
Amortization of intangible assets	205	198
Merger and acquisition integration related (recoveries) expenses	0	$ 0
Litigation accrual	$ 0

The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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