SEGMENT REPORTING - Operating Segments and Reconciliation of Information to Condensed Consolidated Financial Statements (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Segment Reporting Information [Line Items]
Interest income	$ 113,909	$ 114,823	$ 219,945	$ 229,084
Interest expense	7,959	6,777	12,544	16,438
Provision/ (credit) for credit losses	3,046	(4,204)	4,681	(38,912)	$ (45,556)
Non-interest income	35,245	26,259	55,840	55,125
Non-interest expense	64,991	62,975	127,138	131,148
Income before income tax expense	73,158	75,534	131,422	175,535
Income tax expense	18,358	18,271	32,687	42,808
Net income	54,800	57,263	98,735	132,727
Assets	13,303,009	12,925,577	13,303,009	12,925,577	$ 12,590,726
Inter-Segment Elimination
Segment Reporting Information [Line Items]
Interest income	(3)	(3)	(6)	(6)
Interest expense	(3)	(3)	(6)	(6)
Provision/ (credit) for credit losses	0	0	0	0
Non-interest income	(12,482)	(4,217)	(14,790)	(4,434)
Non-interest expense	(204)	(217)	(440)	(434)
Income before income tax expense	(12,278)	(4,000)	(14,350)	(4,000)
Income tax expense	0	0	0	0
Net income	(12,278)	(4,000)	(14,350)	(4,000)
Assets	(89,468)	(64,406)	(89,468)	(64,406)
Community Banking | Operating Segments
Segment Reporting Information [Line Items]
Interest income	113,908	114,823	219,945	229,084
Interest expense	7,962	6,780	12,550	16,444
Provision/ (credit) for credit losses	3,046	(4,204)	4,681	(38,912)
Non-interest income	24,658	23,714	39,713	45,439
Non-interest expense	59,123	58,049	116,502	121,744
Income before income tax expense	68,435	77,912	125,925	175,247
Income tax expense	13,635	17,728	27,190	41,566
Net income	54,800	60,184	98,735	133,681
Assets	13,323,298	12,925,577	13,323,298	12,925,577
Insurance | Operating Segments
Segment Reporting Information [Line Items]
Interest income	1	1	1	2
Interest expense	0	0	0	0
Provision/ (credit) for credit losses	0	0	0	0
Non-interest income	17,513	1,246	19,633	3,397
Non-interest expense	2,387	1,324	3,863	2,811
Income before income tax expense	15,127	(77)	15,771	588
Income tax expense	4,217	(21)	4,397	162
Net income	10,910	(56)	11,374	426
Assets	17,804	8,758	17,804	8,758
Investment Management | Operating Segments
Segment Reporting Information [Line Items]
Interest income	3	2	5	4
Interest expense	0	0	0	0
Provision/ (credit) for credit losses	0	0	0	0
Non-interest income	5,556	5,516	11,284	10,723
Non-interest expense	3,685	3,819	7,213	7,027
Income before income tax expense	1,874	1,699	4,076	3,700
Income tax expense	506	564	1,100	1,080
Net income	1,368	1,135	2,976	2,620
Assets	$ 51,375	$ 55,648	$ 51,375	$ 55,648