SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Impact of Adopting ASU 2016-13 (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses - loans	$ 90,927		$ 57,649	$ 57,649
Allowance for credit losses - unfunded loan commitments			4,064
Commercial real estate
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses - loans	$ 94,133	$ 94,565		61,713	$ 67,289	$ 63,818	$ 66,814
Commercial | Commercial and industrial
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses - loans			22,353
Commercial | Commercial real estate
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses - loans			5,941
Commercial | Multifamily
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses - loans			11,405
Commercial | SBA
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses - loans			3,120
Commercial | Construction
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses - loans			3,906
Consumer | Single family residential mortgage
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses - loans			10,486
Consumer | Other consumer
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses - loans			438
As Reported Under ASC 326
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses - loans			65,258
Allowance for credit losses - unfunded loan commitments			2,838
As Reported Under ASC 326 | Commercial | Commercial and industrial
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses - loans			23,015
As Reported Under ASC 326 | Commercial | Commercial real estate
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses - loans			10,788
As Reported Under ASC 326 | Commercial | Multifamily
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses - loans			13,214
As Reported Under ASC 326 | Commercial | SBA
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses - loans			3,508
As Reported Under ASC 326 | Commercial | Construction
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses - loans			4,009
As Reported Under ASC 326 | Consumer | Single family residential mortgage
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses - loans			10,066
As Reported Under ASC 326 | Consumer | Other consumer
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses - loans			658
Impact of ASC 326 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses - loans			7,609
Allowance for credit losses - unfunded loan commitments			(1,226)
Impact of ASC 326 Adoption | Commercial real estate
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses - loans				$ 6,383			$ 0
Impact of ASC 326 Adoption | Commercial | Commercial and industrial
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses - loans			662
Impact of ASC 326 Adoption | Commercial | Commercial real estate
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses - loans			4,847
Impact of ASC 326 Adoption | Commercial | Multifamily
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses - loans			1,809
Impact of ASC 326 Adoption | Commercial | SBA
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses - loans			388
Impact of ASC 326 Adoption | Commercial | Construction
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses - loans			103
Impact of ASC 326 Adoption | Consumer | Single family residential mortgage
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses - loans			(420)
Impact of ASC 326 Adoption | Consumer | Other consumer
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses - loans			$ 220