ALLOWANCE FOR LOAN AND LEASE LOSSES - Changes in the Allowance for Loan and Lease Losses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for Loan and Lease Losses	$ 14,083	$ 2,303
Loans and Leases Receivable, Allowance	56,722	54,380	$ 56,542	$ 54,021
Allowance for loan and lease losses:
Allowance for Loan and Lease Losses, Write-offs	14,582	3,669
Allowance for Loan and Lease Loss, Recovery of Bad Debts	679	1,725
Total net charge-offs	13,903	1,944
Ending allowance on loans individually evaluated for impairment	1,420		1,160
Ending allowance on loans collectively evaluated for impairment	55,302		55,382
Loans and Leases:
Ending balance of loans individually evaluated for impairment	82,273		86,809
Ending balance of loans collectively evaluated for impairment	8,726,928		8,737,405
Loans and Leases Receivable, Net of Deferred Income	8,809,201		8,824,214
Impaired Financing Receivable, Related Allowance	56,722		56,542
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for Loan and Lease Losses	13,268	889
Loans and Leases Receivable, Allowance	19,926	18,038	18,746	17,598
Allowance for loan and lease losses:
Allowance for Loan and Lease Losses, Write-offs	12,328	885
Allowance for Loan and Lease Loss, Recovery of Bad Debts	240	436
Total net charge-offs	12,088	449
Ending allowance on loans individually evaluated for impairment	738		667
Ending allowance on loans collectively evaluated for impairment	19,188		18,079
Loans and Leases:
Ending balance of loans individually evaluated for impairment	33,424		37,633
Ending balance of loans collectively evaluated for impairment	2,510,003		2,477,028
Loans and Leases Receivable, Net of Deferred Income	2,543,427		2,514,661
Impaired Financing Receivable, Related Allowance	19,926		18,746
Lease financing
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for Loan and Lease Losses	343	(49)
Loans and Leases Receivable, Allowance	1,373	626	1,130	675
Allowance for loan and lease losses:
Allowance for Loan and Lease Losses, Write-offs	(100)	0
Allowance for Loan and Lease Loss, Recovery of Bad Debts	0	0
Total net charge-offs	100	0
Ending allowance on loans individually evaluated for impairment	0		0
Ending allowance on loans collectively evaluated for impairment	1,373		1,130
Loans and Leases:
Ending balance of loans individually evaluated for impairment	301		22
Ending balance of loans collectively evaluated for impairment	95,272		93,393
Loans and Leases Receivable, Net of Deferred Income	95,573		93,415
Impaired Financing Receivable, Related Allowance	1,373		1,130
Construction real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for Loan and Lease Losses	(683)	690
Loans and Leases Receivable, Allowance	2,793	4,267	3,413	3,577
Allowance for loan and lease losses:
Allowance for Loan and Lease Losses, Write-offs	0	0
Allowance for Loan and Lease Loss, Recovery of Bad Debts	63	0
Total net charge-offs	(63)	0
Ending allowance on loans individually evaluated for impairment	0		0
Ending allowance on loans collectively evaluated for impairment	2,793		3,413
Loans and Leases:
Ending balance of loans individually evaluated for impairment	8		9
Ending balance of loans collectively evaluated for impairment	458,105		548,926
Loans and Leases Receivable, Net of Deferred Income	458,113		548,935
Impaired Financing Receivable, Related Allowance	2,793		3,413
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for Loan and Lease Losses	493	815
Loans and Leases Receivable, Allowance	20,400	20,321	21,048	20,930
Allowance for loan and lease losses:
Allowance for Loan and Lease Losses, Write-offs	1,214	2,176
Allowance for Loan and Lease Loss, Recovery of Bad Debts	73	752
Total net charge-offs	1,141	1,424
Ending allowance on loans individually evaluated for impairment	651		461
Ending allowance on loans collectively evaluated for impairment	19,749		20,587
Loans and Leases:
Ending balance of loans individually evaluated for impairment	25,206		25,022
Ending balance of loans collectively evaluated for impairment	3,776,973		3,729,659
Loans and Leases Receivable, Net of Deferred Income	3,802,179		3,754,681
Impaired Financing Receivable, Related Allowance	20,400		21,048
Residential real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for Loan and Lease Losses	125	114
Loans and Leases Receivable, Allowance	5,043	4,727	4,964	4,683
Allowance for loan and lease losses:
Allowance for Loan and Lease Losses, Write-offs	82	96
Allowance for Loan and Lease Loss, Recovery of Bad Debts	36	26
Total net charge-offs	46	70
Ending allowance on loans individually evaluated for impairment	31		32
Ending allowance on loans collectively evaluated for impairment	5,012		4,932
Loans and Leases:
Ending balance of loans individually evaluated for impairment	16,935		17,598
Ending balance of loans collectively evaluated for impairment	958,185		938,048
Loans and Leases Receivable, Net of Deferred Income	975,120		955,646
Impaired Financing Receivable, Related Allowance	5,043		4,964
Home equity
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for Loan and Lease Losses	185	(294)
Loans and Leases Receivable, Allowance	5,250	4,828	5,348	4,935
Allowance for loan and lease losses:
Allowance for Loan and Lease Losses, Write-offs	468	242
Allowance for Loan and Lease Loss, Recovery of Bad Debts	185	429
Total net charge-offs	283	(187)
Ending allowance on loans individually evaluated for impairment	0		0
Ending allowance on loans collectively evaluated for impairment	5,250		5,348
Loans and Leases:
Ending balance of loans individually evaluated for impairment	6,225		6,351
Ending balance of loans collectively evaluated for impairment	790,893		810,931
Loans and Leases Receivable, Net of Deferred Income	797,118		817,282
Impaired Financing Receivable, Related Allowance	5,250		5,348
Installment
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for Loan and Lease Losses	19	(49)
Loans and Leases Receivable, Allowance	380	290	362	307
Allowance for loan and lease losses:
Allowance for Loan and Lease Losses, Write-offs	49	16
Allowance for Loan and Lease Loss, Recovery of Bad Debts	48	48
Total net charge-offs	1	(32)
Ending allowance on loans individually evaluated for impairment	0		0
Ending allowance on loans collectively evaluated for impairment	380		362
Loans and Leases:
Ending balance of loans individually evaluated for impairment	174		174
Ending balance of loans collectively evaluated for impairment	90,515		93,038
Loans and Leases Receivable, Net of Deferred Income	90,689		93,212
Impaired Financing Receivable, Related Allowance	380		362
Credit card
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for Loan and Lease Losses	333	187
Loans and Leases Receivable, Allowance	1,557	1,283	1,531	$ 1,316
Allowance for loan and lease losses:
Allowance for Loan and Lease Losses, Write-offs	341	254
Allowance for Loan and Lease Loss, Recovery of Bad Debts	34	34
Total net charge-offs	(307)	$ (220)
Ending allowance on loans individually evaluated for impairment	0		0
Ending allowance on loans collectively evaluated for impairment	1,557		1,531
Loans and Leases:
Ending balance of loans individually evaluated for impairment	0		0
Ending balance of loans collectively evaluated for impairment	46,982		46,382
Loans and Leases Receivable, Net of Deferred Income	46,982		46,382
Impaired Financing Receivable, Related Allowance	$ 1,557		$ 1,531