SEGMENT REPORTING (Operating Segments and Reconciliation of Information to Condensed Consolidated Financial Statements) (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Interest income	$ 114,261	$ 83,858
Interest expense	9,661	19,524
Provision/ (credit) for credit losses	(34,708)	24,469	$ 85,669
Non-interest income	28,866	18,168
Non-interest expense	68,173	47,746
Income before income tax expense	100,001	10,287
Income tax expense	24,537	300
Net income	75,464	9,987
Assets	12,873,366	8,929,602	$ 12,798,429
Inter-Segment Elimination
Segment Reporting Information [Line Items]
Interest income	(3)	(4)
Interest expense	(3)	(4)
Provision/ (credit) for credit losses	0	0
Non-interest income	(217)	(204)
Non-interest expense	(217)	(204)
Income before income tax expense	0	0
Income tax expense	0	0
Net income	0	0
Assets	(73,137)	(54,791)
Community Banking | Operating Segments
Segment Reporting Information [Line Items]
Interest income	114,261	83,857
Interest expense	9,664	19,528
Provision/ (credit) for credit losses	(34,708)	24,469
Non-interest income	21,725	13,977
Non-interest expense	63,695	44,655
Income before income tax expense	97,335	9,182
Income tax expense	23,838	1
Net income	73,497	9,181
Assets	12,878,311	8,917,849
Insurance | Operating Segments
Segment Reporting Information [Line Items]
Interest income	1	3
Interest expense	0	0
Provision/ (credit) for credit losses	0	0
Non-interest income	2,151	2,129
Non-interest expense	1,487	1,464
Income before income tax expense	665	668
Income tax expense	183	185
Net income	482	483
Assets	11,504	10,887
Investment Management | Operating Segments
Segment Reporting Information [Line Items]
Interest income	2	2
Interest expense	0	0
Provision/ (credit) for credit losses	0	0
Non-interest income	5,207	2,266
Non-interest expense	3,208	1,831
Income before income tax expense	2,001	437
Income tax expense	516	114
Net income	1,485	323
Assets	$ 56,688	$ 55,657