LOANS AND ALLOWANCE FOR CREDIT LOSSES - Allowance for Loan Losses and Recorded Investment Excluding Accrued Interest in Loans (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	$ 57,649
Provision (reversal of provision)	29,719	$ 35,829	$ 31,121
Balance at end of year	81,030	57,649
Commercial real estate
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	61,713	66,814	53,049
Charge-offs	(15,417)	(41,766)	(18,499)
Recoveries	1,815	836	1,143
Net (charge-offs) recoveries	(13,602)	(40,930)	(17,356)
Provision (reversal of provision)	29,719	35,829	31,121
Balance at end of year	84,213	61,713	66,814
Commercial real estate \| Impact of ASC 326 Adoption
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	6,383	0	0
Balance at end of year		6,383	0
Allowance for Loan Losses
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	57,649	62,192
Charge-offs	(15,417)	(41,766)
Recoveries	1,815	836
Net (charge-offs) recoveries	(13,602)	(40,930)
Provision (reversal of provision)	29,374	36,387
Balance at end of year	81,030	57,649	62,192
Allowance for Loan Losses \| Impact of ASC 326 Adoption
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	7,609
Balance at end of year		7,609
Allowance for Loan Losses \| Commercial real estate
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	57,649	62,192	49,333
Charge-offs	(15,417)	(41,766)	(18,499)
Recoveries	1,815	836	1,143
Net (charge-offs) recoveries	(13,602)	(40,930)	(17,356)
Provision (reversal of provision)	29,374	36,387	30,215
Balance at end of year	81,030	57,649	62,192
Allowance for Loan Losses \| Commercial real estate \| Impact of ASC 326 Adoption
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	7,609	0	0
Balance at end of year		7,609	0
Allowance for Loan Losses \| Commercial \| Commercial and industrial
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	22,353	18,191
Charge-offs	(13,588)	(36,787)
Recoveries	604	138
Net (charge-offs) recoveries	(12,984)	(36,649)
Provision (reversal of provision)	10,577	40,811
Balance at end of year	20,608	22,353	18,191
Allowance for Loan Losses \| Commercial \| Commercial and industrial \| Impact of ASC 326 Adoption
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	662
Balance at end of year		662
Allowance for Loan Losses \| Commercial \| Commercial real estate
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	5,941	6,674
Charge-offs	0	0
Recoveries	0	0
Net (charge-offs) recoveries	0	0
Provision (reversal of provision)	8,286	(733)
Balance at end of year	19,074	5,941	6,674
Allowance for Loan Losses \| Commercial \| Commercial real estate \| Impact of ASC 326 Adoption
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	4,847
Balance at end of year		4,847
Allowance for Loan Losses \| Commercial \| Multifamily
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	11,405	17,970
Charge-offs	0	(6)
Recoveries	0	0
Net (charge-offs) recoveries	0	(6)
Provision (reversal of provision)	9,298	(6,559)
Balance at end of year	22,512	11,405	17,970
Allowance for Loan Losses \| Commercial \| Multifamily \| Impact of ASC 326 Adoption
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	1,809
Balance at end of year		1,809
Allowance for Loan Losses \| Commercial \| SBA
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	3,120	1,827
Charge-offs	(1,083)	(2,121)
Recoveries	328	217
Net (charge-offs) recoveries	(755)	(1,904)
Provision (reversal of provision)	392	3,197
Balance at end of year	3,145	3,120	1,827
Allowance for Loan Losses \| Commercial \| SBA \| Impact of ASC 326 Adoption
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	388
Balance at end of year		388
Allowance for Loan Losses \| Commercial \| Construction
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	3,906	3,461
Charge-offs	0	(371)
Recoveries	0	0
Net (charge-offs) recoveries	0	(371)
Provision (reversal of provision)	1,840	816
Balance at end of year	5,849	3,906	3,461
Allowance for Loan Losses \| Commercial \| Construction \| Impact of ASC 326 Adoption
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	103
Balance at end of year		103
Allowance for Loan Losses \| Commercial \| Lease financing
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	0	0
Charge-offs		0
Recoveries		12
Net (charge-offs) recoveries		12
Provision (reversal of provision)		(12)
Balance at end of year		0	0
Allowance for Loan Losses \| Consumer \| Single Family Residential Mortgage
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	10,486	13,128
Charge-offs	(742)	(2,369)
Recoveries	664	150
Net (charge-offs) recoveries	(78)	(2,219)
Provision (reversal of provision)	(797)	(423)
Balance at end of year	9,191	10,486	13,128
Allowance for Loan Losses \| Consumer \| Single Family Residential Mortgage \| Impact of ASC 326 Adoption
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	(420)
Balance at end of year		(420)
Allowance for Loan Losses \| Consumer \| Other Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	438	941
Charge-offs	(4)	(112)
Recoveries	219	319
Net (charge-offs) recoveries	215	207
Provision (reversal of provision)	(222)	(710)
Balance at end of year	651	438	941
Allowance for Loan Losses \| Consumer \| Other Consumer \| Impact of ASC 326 Adoption
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	220
Balance at end of year		220
Reserve for Unfunded Loan Commit-ments \| Commercial real estate
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	4,064	4,622	3,716
Charge-offs	0	0	0
Recoveries	0	0	0
Net (charge-offs) recoveries	0	0	0
Provision (reversal of provision)	345	(558)	906
Balance at end of year	3,183	4,064	4,622
Reserve for Unfunded Loan Commit-ments \| Commercial real estate \| Impact of ASC 326 Adoption
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of year	$ (1,226)	0	0
Balance at end of year		$ (1,226)	$ 0

Amount, after recovery, of writeoff of financing receivable, charged against allowance for credit loss.

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

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Amount of increase in allowance for credit loss on financing receivable from recovery.

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Amount of writeoff of financing receivable, charged against allowance for credit loss.

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Amount of credit loss expense (reversal of expense) for financing receivable.

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