LOANS AND CREDIT QUALITY - Collateral Dependent Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	$ 5,432,278	$ 5,114,556
Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	1,467,923	1,626,082
Consumer loans [Member] | Single family [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	983,166	1,072,706
Consumer loans [Member] | Home equity and other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	484,757	553,376
Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	3,966,634
Commercial loans [Member] | Commercial and Industrial Sector [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	1,160,243	892,026
Commercial loans [Member] | Owner occupied commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	462,903	477,316
Commercial loans [Member] | Commercial business [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	697,340	$ 414,710
Land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	3,576
Land | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	0
Land | Consumer loans [Member] | Single family [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	0
Land | Consumer loans [Member] | Home equity and other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	0
Land | Commercial loans [Member] | Commercial and Industrial Sector [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	3,576
Land | Commercial loans [Member] | Owner occupied commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	1,789
Land | Commercial loans [Member] | Commercial business [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	1,787
1-4 Family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	1,527
1-4 Family | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	812
1-4 Family | Consumer loans [Member] | Single family [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	812
1-4 Family | Consumer loans [Member] | Home equity and other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	0
1-4 Family | Commercial loans [Member] | Commercial and Industrial Sector [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	715
1-4 Family | Commercial loans [Member] | Owner occupied commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	0
1-4 Family | Commercial loans [Member] | Commercial business [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	715
Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	0
Multifamily | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	0
Multifamily | Consumer loans [Member] | Single family [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	0
Multifamily | Consumer loans [Member] | Home equity and other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	0
Multifamily | Commercial loans [Member] | Commercial and Industrial Sector [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	0
Multifamily | Commercial loans [Member] | Owner occupied commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	0
Multifamily | Commercial loans [Member] | Commercial business [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	0
Non-residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	4,535
Non-residential real estate | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	0
Non-residential real estate | Consumer loans [Member] | Single family [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	0
Non-residential real estate | Consumer loans [Member] | Home equity and other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	0
Non-residential real estate | Commercial loans [Member] | Commercial and Industrial Sector [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	4,535
Non-residential real estate | Commercial loans [Member] | Owner occupied commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	4,305
Non-residential real estate | Commercial loans [Member] | Commercial business [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	230
Other non-real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	7,786
Other non-real estate | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	0
Other non-real estate | Consumer loans [Member] | Single family [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	0
Other non-real estate | Consumer loans [Member] | Home equity and other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	0
Other non-real estate | Commercial loans [Member] | Commercial and Industrial Sector [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	7,786
Other non-real estate | Commercial loans [Member] | Owner occupied commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	0
Other non-real estate | Commercial loans [Member] | Commercial business [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	7,786
Total
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	17,424
Total | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	812
Total | Consumer loans [Member] | Single family [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	812
Total | Consumer loans [Member] | Home equity and other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	0
Total | Commercial loans [Member] | Commercial and Industrial Sector [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	16,612
Total | Commercial loans [Member] | Owner occupied commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	6,094
Total | Commercial loans [Member] | Commercial business [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total LHFI	$ 10,518