ALLOWANCE FOR CREDIT LOSSES AND CREDIT QUALITY INFORMATION - Schedule of Allowance for Loan Losses and Loan Balances (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Allowance for credit losses
Beginning Balance	$ 228,804	$ 47,576
Charge-offs	(5,476)	(4,455)
Recoveries	1,650	3,451
(Recovery of) provision for credit losses	(20,160)	56,646
Ending balance	204,818	139,073
Loans evaluated on an individual basis	12	20
Loans evaluated on a collective basis	204,806	139,053
Loans individually evaluated for impairment	38,334	26,895
Loans evaluated on a collective basis	8,530,808	8,508,091
Ending balance	8,569,142	8,534,986	$ 9,014,677
Reverse mortgage, fair value	9,400	15,800	10,100
Loans purchased with credit deterioration		100
Impact of adoption ASC 326
Allowance for credit losses
Beginning Balance		35,855
Commercial \| Commercial and industrial
Allowance for credit losses
Beginning Balance	150,875	22,849
Charge-offs	(5,052)	(3,064)
Recoveries	1,140	2,847
(Recovery of) provision for credit losses	(21,093)	23,392
Ending balance	125,870	65,771
Loans evaluated on an individual basis	1	20
Loans evaluated on a collective basis	125,869	65,751
Loans individually evaluated for impairment	20,902	8,843
Loans evaluated on a collective basis	2,642,570	2,289,529
Ending balance	2,663,472	2,298,372	2,949,303
Commercial \| Commercial and industrial \| Impact of adoption ASC 326
Allowance for credit losses
Beginning Balance		19,747
Commercial \| Owner-occupied commercial
Allowance for credit losses
Beginning Balance	9,615	4,616
Charge-offs	0	(283)
Recoveries	90	125
(Recovery of) provision for credit losses	(88)	6,555
Ending balance	9,617	9,541
Loans evaluated on an individual basis	0	0
Loans evaluated on a collective basis	9,617	9,541
Loans individually evaluated for impairment	5,118	4,818
Loans evaluated on a collective basis	1,328,871	1,308,375
Ending balance	1,333,989	1,313,193	1,332,727
Commercial \| Owner-occupied commercial \| Impact of adoption ASC 326
Allowance for credit losses
Beginning Balance		(1,472)
Commercial \| Commercial mortgages
Allowance for credit losses
Beginning Balance	31,071	7,452
Charge-offs	0	(51)
Recoveries	14	29
(Recovery of) provision for credit losses	(540)	17,508
Ending balance	30,545	26,600
Loans evaluated on an individual basis	11	0
Loans evaluated on a collective basis	30,534	26,600
Loans individually evaluated for impairment	4,280	4,691
Loans evaluated on a collective basis	1,971,686	2,218,426
Ending balance	1,975,966	2,223,117	2,086,062
Commercial \| Commercial mortgages \| Impact of adoption ASC 326
Allowance for credit losses
Beginning Balance		1,662
Commercial \| Construction
Allowance for credit losses
Beginning Balance	12,190	3,891
Charge-offs	0	0
Recoveries	0	5
(Recovery of) provision for credit losses	2,097	621
Ending balance	14,287	5,198
Loans evaluated on an individual basis	0	0
Loans evaluated on a collective basis	14,287	5,198
Loans individually evaluated for impairment	72	96
Loans evaluated on a collective basis	784,029	626,157
Ending balance	784,101	626,253	716,275
Commercial \| Construction \| Impact of adoption ASC 326
Allowance for credit losses
Beginning Balance		681
Residential
Allowance for credit losses
Beginning Balance	6,893	1,381
Charge-offs	0	(143)
Recoveries	140	91
(Recovery of) provision for credit losses	(1,331)	2,742
Ending balance	5,702	11,593
Loans evaluated on an individual basis	0	0
Loans evaluated on a collective basis	5,702	11,593
Loans individually evaluated for impairment	5,649	6,152
Loans evaluated on a collective basis	665,931	949,613
Ending balance	671,580	955,765	764,393
Residential \| Impact of adoption ASC 326
Allowance for credit losses
Beginning Balance		7,522
Consumer
Allowance for credit losses
Beginning Balance	18,160	7,387
Charge-offs	(424)	(914)
Recoveries	266	354
(Recovery of) provision for credit losses	795	5,828
Ending balance	18,797	20,370
Loans evaluated on an individual basis	0	0
Loans evaluated on a collective basis	18,797	20,370
Loans individually evaluated for impairment	2,313	2,295
Loans evaluated on a collective basis	1,137,721	1,115,991
Ending balance	$ 1,140,034	1,118,286	$ 1,165,917
Consumer \| Impact of adoption ASC 326
Allowance for credit losses
Beginning Balance		$ 7,715

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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Amount, before allowance for credit loss, of financing receivable.

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