COMMITMENTS AND CONTINGENCIES (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Other Commitments [Line Items]
Unused Commitments to Extend Credit	$ 3,038,659		$ 3,038,659		$ 2,853,059
Loans and Leases Receivable, Net of Deferred Income	9,511,510		9,511,510		9,900,970
Amortization Method Qualified Affordable Housing Project Investments	107,246		107,246		100,417
Qualified Affordable Housing Project Investments, Commitment	47,601		47,601		55,556
Investment Holdings [Line Items]
Amortization Method Qualified Affordable Housing Project Investments, Amortization	3,579	$ 2,130	5,824	$ 4,332
Affordable Housing Tax Credits and Other Tax Benefits, Amount	(3,334)	(2,013)	(5,649)	(4,082)
Low Income Housing Tax Credits
Other Commitments [Line Items]
Amortization Method Qualified Affordable Housing Project Investments	85,395		85,395		90,401
Qualified Affordable Housing Project Investments, Commitment	39,297		39,297		47,531
Investment Holdings [Line Items]
Amortization Method Qualified Affordable Housing Project Investments, Amortization	2,423	2,024	4,460	4,104
Affordable Housing Tax Credits and Other Tax Benefits, Amount	(2,154)	(1,887)	(4,338)	(3,831)
Historic tax credit [Member]
Other Commitments [Line Items]
Amortization Method Qualified Affordable Housing Project Investments	3,478		3,478		3,607
Qualified Affordable Housing Project Investments, Commitment	364		364		364
Investment Holdings [Line Items]
Amortization Method Qualified Affordable Housing Project Investments, Amortization	64	62	219	140
Affordable Housing Tax Credits and Other Tax Benefits, Amount	(80)	(82)	(159)	(163)
New Markets Tax Credit
Other Commitments [Line Items]
Amortization Method Qualified Affordable Housing Project Investments	4,251		4,251		1,165
Qualified Affordable Housing Project Investments, Commitment	0		0		0
Investment Holdings [Line Items]
Amortization Method Qualified Affordable Housing Project Investments, Amortization	52	44	105	88
Affordable Housing Tax Credits and Other Tax Benefits, Amount	(53)	(44)	(105)	(88)
Renewable Energy Program
Other Commitments [Line Items]
Amortization Method Qualified Affordable Housing Project Investments	14,122		14,122		5,244
Qualified Affordable Housing Project Investments, Commitment	7,940		7,940		7,661
Investment Holdings [Line Items]
Amortization Method Qualified Affordable Housing Project Investments, Amortization	1,040	0	1,040	0
Affordable Housing Tax Credits and Other Tax Benefits, Amount	(1,047)	$ 0	(1,047)	$ 0
Commercial
Other Commitments [Line Items]
Unused Commitments to Extend Credit	1,391,522		1,391,522		1,270,765
Loans and Leases Receivable, Net of Deferred Income	2,701,203		2,701,203		3,007,509
Lease financing
Other Commitments [Line Items]
Unused Commitments to Extend Credit	10,000		10,000		0
Loans and Leases Receivable, Net of Deferred Income	68,229		68,229		72,987
Construction real estate
Other Commitments [Line Items]
Unused Commitments to Extend Credit	356,390		356,390		374,008
Loans and Leases Receivable, Net of Deferred Income	630,329		630,329		636,096
Commercial real estate - investor
Other Commitments [Line Items]
Unused Commitments to Extend Credit	172,320		172,320		139,754
Loans and Leases Receivable, Net of Deferred Income	3,318,836		3,318,836		3,244,540
Commercial real estate-owner
Other Commitments [Line Items]
Unused Commitments to Extend Credit	36,212		36,212		51,637
Loans and Leases Receivable, Net of Deferred Income	1,013,725		1,013,725		1,063,318
Residential real estate
Other Commitments [Line Items]
Unused Commitments to Extend Credit	37,246		37,246		28,895
Loans and Leases Receivable, Net of Deferred Income	932,112		932,112		1,003,086
Home equity
Other Commitments [Line Items]
Unused Commitments to Extend Credit	804,275		804,275		762,406
Loans and Leases Receivable, Net of Deferred Income	711,756		711,756		743,099
Installment
Other Commitments [Line Items]
Unused Commitments to Extend Credit	15,525		15,525		18,229
Loans and Leases Receivable, Net of Deferred Income	89,143		89,143		81,850
Credit card
Other Commitments [Line Items]
Unused Commitments to Extend Credit	215,169		215,169		207,365
Loans and Leases Receivable, Net of Deferred Income	$ 46,177		$ 46,177		$ 48,485