ALLOWANCE FOR CREDIT LOSSES - Changes in the Allowance for Credit Losses (Details) - USD ($) $ in Thousands		3 Months Ended
	Jan. 01, 2020	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Balance at beginning of year	$ 57,650	$ 57,650	$ 56,542
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	61,505	61,505
Provision for Credit Losses		23,880	14,083
Loans charged off		(1,849)	(14,582)
Recoveries		2,699	679
Total net charge-offs		850	(13,903)
Balance at end of year	119,155	143,885	56,722
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		9,307,819		9,201,665
Commercial
Financing Receivable, Allowance for Credit Loss [Line Items]
Balance at beginning of year	18,584	18,584	18,746
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	9,901	9,901
Provision for Credit Losses		16,016	13,268
Loans charged off		(1,091)	(12,328)
Recoveries		2,000	240
Total net charge-offs		909	(12,088)
Balance at end of year	28,485	45,410	19,926
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	971	1,130
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	118	118
Provision for Credit Losses		405	343
Loans charged off		0	(100)
Recoveries		0	0
Total net charge-offs		0	(100)
Balance at end of year	1,089	1,494	1,373
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	2,381	3,413
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	11,579	11,579
Provision for Credit Losses		(449)	(683)
Loans charged off		0	0
Recoveries		0	63
Total net charge-offs		0	63
Balance at end of year	13,960	13,511	2,793
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	23,579	21,048
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	24,118	24,118
Provision for Credit Losses		5,227	493
Loans charged off		(4)	(1,214)
Recoveries		234	73
Total net charge-offs		230	(1,141)
Balance at end of year	47,697	53,154	20,400
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	5,299	4,964
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	5,490	5,490
Provision for Credit Losses		558	125
Loans charged off		(115)	(82)
Recoveries		52	36
Total net charge-offs		(63)	(46)
Balance at end of year	10,789	11,284	5,043
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	4,787	5,348
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	8,430	8,430
Provision for Credit Losses		1,538	185
Loans charged off		(267)	(468)
Recoveries		339	185
Total net charge-offs		72	(283)
Balance at end of year	13,217	14,827	5,250
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	392	362
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	801	801
Provision for Credit Losses		75	19
Loans charged off		(61)	(49)
Recoveries		31	48
Total net charge-offs		(30)	(1)
Balance at end of year	1,193	1,238	380
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	1,657	1,531
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method	1,068	1,068
Provision for Credit Losses		510	333
Loans charged off		(311)	(341)
Recoveries		43	34
Total net charge-offs		268	307
Balance at end of year	$ 2,725	$ 2,967	$ 1,557
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