ALLOWANCE FOR CREDIT LOSSES - Changes in the Allowance for Credit Losses (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Jan. 01, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Balance at beginning of year	$ 57,650	$ 143,885	$ 56,722	$ 57,650	$ 56,542
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	61,505			61,505
Provision for Credit Losses		17,859	6,658	41,739	20,741
Loans charged off		(4,136)	(3,165)	(5,985)	(17,747)
Recoveries		1,053	1,334	3,752	2,013
Total net charge-offs		(3,083)	(1,831)	(2,233)	(15,734)
Balance at end of year	119,155	158,661	61,549	158,661	61,549
Allowance for credit losses:
Ending allowance on loans individually evaluated for impairment						$ 2,175
Ending allowance on loans collectively evaluated for impairment						55,475
Impaired Financing Receivable, Related Allowance						57,650
Loans and Leases:
Ending balance of loans individually evaluated for impairment						59,600
Ending balance of loans collectively evaluated for impairment						9,142,065
Loans and Leases Receivable, Net of Deferred Income		10,181,711		10,181,711		9,201,665
Commercial
Financing Receivable, Allowance for Credit Loss [Line Items]
Balance at beginning of year	18,584	45,410	19,926	18,584	18,746
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	9,901			9,901
Provision for Credit Losses		6,018	6,242	22,034	19,510
Loans charged off		(1,282)	(1,873)	(2,373)	(14,201)
Recoveries		275	291	2,275	531
Total net charge-offs		(1,007)	(1,582)	(98)	(13,670)
Balance at end of year	28,485	50,421	24,586	50,421	24,586
Allowance for credit losses:
Ending allowance on loans individually evaluated for impairment						2,044
Ending allowance on loans collectively evaluated for impairment						16,540
Impaired Financing Receivable, Related Allowance						18,584
Loans and Leases:
Ending balance of loans individually evaluated for impairment						27,480
Ending balance of loans collectively evaluated for impairment						2,438,397
Loans and Leases Receivable, Net of Deferred Income						2,465,877
Lease financing
Financing Receivable, Allowance for Credit Loss [Line Items]
Balance at beginning of year	971	1,494	1,373	971	1,130
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	118			118
Provision for Credit Losses		(63)	20	342	363
Loans charged off		0	0	0	(100)
Recoveries		0	0	0	0
Total net charge-offs		0	0	0	(100)
Balance at end of year	1,089	1,431	1,393	1,431	1,393
Allowance for credit losses:
Ending allowance on loans individually evaluated for impairment						0
Ending allowance on loans collectively evaluated for impairment						971
Impaired Financing Receivable, Related Allowance						971
Loans and Leases:
Ending balance of loans individually evaluated for impairment						223
Ending balance of loans collectively evaluated for impairment						88,141
Loans and Leases Receivable, Net of Deferred Income						88,364
Construction real estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Balance at beginning of year	2,381	13,511	2,793	2,381	3,413
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	11,579			11,579
Provision for Credit Losses		1,832	121	1,383	(562)
Loans charged off		0	0	0	0
Recoveries		14	5	14	68
Total net charge-offs		14	5	14	68
Balance at end of year	13,960	15,357	2,919	15,357	2,919
Allowance for credit losses:
Ending allowance on loans individually evaluated for impairment						0
Ending allowance on loans collectively evaluated for impairment						2,381
Impaired Financing Receivable, Related Allowance						2,381
Loans and Leases:
Ending balance of loans individually evaluated for impairment						0
Ending balance of loans collectively evaluated for impairment						493,182
Loans and Leases Receivable, Net of Deferred Income						493,182
Commercial real estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Balance at beginning of year	23,579	53,154	20,400	23,579	21,048
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	24,118			24,118
Provision for Credit Losses		10,799	(211)	16,026	282
Loans charged off		(2,037)	(86)	(2,041)	(1,300)
Recoveries		424	254	658	327
Total net charge-offs		(1,613)	168	(1,383)	(973)
Balance at end of year	47,697	62,340	20,357	62,340	20,357
Allowance for credit losses:
Ending allowance on loans individually evaluated for impairment						113
Ending allowance on loans collectively evaluated for impairment						23,466
Impaired Financing Receivable, Related Allowance						23,579
Loans and Leases:
Ending balance of loans individually evaluated for impairment						10,831
Ending balance of loans collectively evaluated for impairment						4,183,820
Loans and Leases Receivable, Net of Deferred Income						4,194,651
Residential real estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Balance at beginning of year	5,299	11,284	5,043	5,299	4,964
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	5,490			5,490
Provision for Credit Losses		(648)	14	(90)	139
Loans charged off		(148)	(150)	(263)	(232)
Recoveries		93	101	145	137
Total net charge-offs		(55)	(49)	(118)	(95)
Balance at end of year	10,789	10,581	5,008	10,581	5,008
Allowance for credit losses:
Ending allowance on loans individually evaluated for impairment						18
Ending allowance on loans collectively evaluated for impairment						5,281
Impaired Financing Receivable, Related Allowance						5,299
Loans and Leases:
Ending balance of loans individually evaluated for impairment						15,162
Ending balance of loans collectively evaluated for impairment						1,040,787
Loans and Leases Receivable, Net of Deferred Income						1,055,949
Home equity
Financing Receivable, Allowance for Credit Loss [Line Items]
Balance at beginning of year	4,787	14,827	5,250	4,787	5,348
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	8,430			8,430
Provision for Credit Losses		(319)	174	1,219	359
Loans charged off		(428)	(689)	(695)	(1,157)
Recoveries		156	572	495	757
Total net charge-offs		(272)	(117)	(200)	(400)
Balance at end of year	13,217	14,236	5,307	14,236	5,307
Allowance for credit losses:
Ending allowance on loans individually evaluated for impairment						0
Ending allowance on loans collectively evaluated for impairment						4,787
Impaired Financing Receivable, Related Allowance						4,787
Loans and Leases:
Ending balance of loans individually evaluated for impairment						5,700
Ending balance of loans collectively evaluated for impairment						766,169
Loans and Leases Receivable, Net of Deferred Income						771,869
Installment
Allowance for credit losses:
Ending allowance on loans individually evaluated for impairment						0
Ending allowance on loans collectively evaluated for impairment						392
Impaired Financing Receivable, Related Allowance						392
Loans and Leases:
Ending balance of loans individually evaluated for impairment						204
Ending balance of loans collectively evaluated for impairment						82,385
Loans and Leases Receivable, Net of Deferred Income						82,589
Installment
Financing Receivable, Allowance for Credit Loss [Line Items]
Balance at beginning of year	392	1,238	380	392	362
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	801			801
Provision for Credit Losses		(32)	32	43	51
Loans charged off		(7)	(78)	(68)	(127)
Recoveries		27	61	58	109
Total net charge-offs		20	(17)	(10)	(18)
Balance at end of year	1,193	1,226	395	1,226	395
Allowance for credit losses:
Ending allowance on loans individually evaluated for impairment						0
Loans and Leases:
Loans and Leases Receivable, Net of Deferred Income						1,959,591
Credit card
Financing Receivable, Allowance for Credit Loss [Line Items]
Balance at beginning of year	1,657	2,967	1,557	1,657	1,531
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	1,068			1,068
Provision for Credit Losses		272	266	782	599
Loans charged off		(234)	(289)	(545)	(630)
Recoveries		64	50	107	84
Total net charge-offs		170	239	438	546
Balance at end of year	$ 2,725	$ 3,069	$ 1,584	$ 3,069	$ 1,584
Allowance for credit losses:
Ending allowance on loans individually evaluated for impairment						0
Ending allowance on loans collectively evaluated for impairment						1,657
Impaired Financing Receivable, Related Allowance						1,657
Loans and Leases:
Ending balance of loans individually evaluated for impairment						0
Ending balance of loans collectively evaluated for impairment						49,184
Loans and Leases Receivable, Net of Deferred Income						$ 49,184