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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Interest income	$ 114,927	$ 87,214	$ 198,785	$ 175,397
Interest expense	13,413	21,029	32,937	42,462
Provision for credit losses	58,686	1,633	83,155	1,505	$ 4,684
Noninterest income	22,924	16,556	41,092	33,525
Noninterest expense	85,438	43,887	133,184	88,079
Income/ (loss) before income taxes	(19,686)	37,221	(9,399)	76,876
Income tax expense	(5,348)	8,945	(5,048)	18,283
Net income/ (loss)	(14,338)	28,276	(4,351)	58,593
Assets	13,290,447	8,398,519	13,290,447	8,398,519	$ 8,629,002
Intersegment Elimination
Segment Reporting Information [Line Items]
Interest income	(3)	(4)	(7)	(7)
Interest expense	(3)	(4)	(7)	(7)
Provision for credit losses	0	0	0	0
Noninterest income	(220)	(166)	(424)	(333)
Noninterest expense	(220)	(166)	(424)	(333)
Income/ (loss) before income taxes	0	0	0	0
Income tax expense	0	0	0	0
Net income/ (loss)	0	0	0	0
Assets	(56,892)	(31,549)	(56,892)	(31,549)
Community Banking
Segment Reporting Information [Line Items]
Interest income	114,929	87,214	198,786	175,397
Interest expense	13,416	21,033	32,944	42,469
Provision for credit losses	58,686	1,633	83,155	1,505
Noninterest income	19,253	12,856	33,230	25,563
Noninterest expense	82,410	40,859	127,065	82,070
Income/ (loss) before income taxes	(20,330)	36,545	(11,148)	74,916
Income tax expense	(5,517)	8,769	(5,516)	17,762
Net income/ (loss)	(14,813)	27,776	(5,632)	57,154
Assets	13,281,483	8,398,263	13,281,483	8,398,263
Insurance
Segment Reporting Information [Line Items]
Interest income	1	1	4	2
Interest expense	0	0	0	0
Provision for credit losses	0	0	0	0
Noninterest income	1,198	1,269	3,327	3,173
Noninterest expense	1,275	1,304	2,739	2,724
Income/ (loss) before income taxes	(76)	(34)	592	451
Income tax expense	(21)	(8)	164	127
Net income/ (loss)	(55)	(26)	428	324
Assets	10,537	11,552	10,537	11,552
Investment Management
Segment Reporting Information [Line Items]
Interest income	0	3	2	5
Interest expense	0	0	0	0
Provision for credit losses	0	0	0	0
Noninterest income	2,693	2,597	4,959	5,122
Noninterest expense	1,973	1,890	3,804	3,618
Income/ (loss) before income taxes	720	710	1,157	1,509
Income tax expense	190	184	304	394
Net income/ (loss)	530	526	853	1,115
Assets	$ 55,319	$ 20,253	$ 55,319	$ 20,253