LOANS RECEIVABLE AND CREDIT QUALITY, Credit Quality Indicators (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	$ 5,806,933	$ 5,633,007
C&I	68,199	2,058
Total	5,875,132
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	5,852,593
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	4,478
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	18,061
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total	0
Real Estate Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	5,806,933	5,633,007
Real Estate Loan [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	5,784,394	5,606,870
Real Estate Loan [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	4,478	4,760
Real Estate Loan [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	18,061	21,377
Real Estate Loan [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	0	0
Real Estate Loan [Member] | One- to Four-Family Residential, Including Condominium and Cooperative Apartment [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	70,982	74,022
Real Estate Loan [Member] | One- to Four-Family Residential, Including Condominium and Cooperative Apartment [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	69,688	72,325
Real Estate Loan [Member] | One- to Four-Family Residential, Including Condominium and Cooperative Apartment [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	182	212
Real Estate Loan [Member] | One- to Four-Family Residential, Including Condominium and Cooperative Apartment [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	1,112	1,485
Real Estate Loan [Member] | One- to Four-Family Residential, Including Condominium and Cooperative Apartment [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	0	0
Real Estate Loan [Member] | Multifamily Residential and Residential Mixed Use [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	4,756,180	4,600,526
Real Estate Loan [Member] | Multifamily Residential and Residential Mixed Use [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	4,747,233	4,589,838
Real Estate Loan [Member] | Multifamily Residential and Residential Mixed Use [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	3,432	3,488
Real Estate Loan [Member] | Multifamily Residential and Residential Mixed Use [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	5,515	7,200
Real Estate Loan [Member] | Multifamily Residential and Residential Mixed Use [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	0	0
Real Estate Loan [Member] | Commercial Mixed Use Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	404,926	404,139
Real Estate Loan [Member] | Commercial Mixed Use Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	399,960	398,139
Real Estate Loan [Member] | Commercial Mixed Use Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	0	535
Real Estate Loan [Member] | Commercial Mixed Use Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	4,966	5,465
Real Estate Loan [Member] | Commercial Mixed Use Real Estate [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	0	0
Real Estate Loan [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	570,845	554,320
Real Estate Loan [Member] | Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	563,513	546,568
Real Estate Loan [Member] | Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	864	525
Real Estate Loan [Member] | Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	6,468	7,227
Real Estate Loan [Member] | Commercial Real Estate [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	0	0
Real Estate Loan [Member] | ADC [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	4,000
Real Estate Loan [Member] | ADC [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	4,000
Real Estate Loan [Member] | ADC [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	0
Real Estate Loan [Member] | ADC [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	0
Real Estate Loan [Member] | ADC [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Real estate loans	0
C & I Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
C&I	68,199	2,058
C & I Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
C&I	68,199
C & I Loans [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
C&I	0
C & I Loans [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
C&I	0
C & I Loans [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
C&I	0
Consumer Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Consumer loans	1,749	3,415	[1]
Consumer Loans [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Consumer loans	1,748	3,414	[1]
Consumer Loans [Member] | Non-Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Consumer loans	$ 1	$ 1	[1]

[1] Included in the balance of consumer loans at December 31, 2016 are $2,058 of C&I loans. Subsequent to December 31, 2016, C&I loans were evaluated based on risk ratings and included in the preceding credit risk profile table.