LOANS RECEIVABLE AND CREDIT QUALITY, Credit Quality Indicators (Details) - USD ($) $ in Thousands		Sep. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans		$ 5,488,491	$ 4,695,186
Total consumer loans		1,675	1,590
Real Estate Loan [Member] | Not Graded [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans	[1]		7,698
Real Estate Loan [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans		5,460,288	4,647,906
Real Estate Loan [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans		6,660	17,183
Real Estate Loan [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans		21,543	22,399
Real Estate Loan [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total 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]
Total real estate loans		75,297	72,095
Real Estate Loan [Member] | One- to Four-Family Residential, Including Condominium and Cooperative Apartment [Member] | Not Graded [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans	[1]		7,698
Real Estate Loan [Member] | One- to Four-Family Residential, Including Condominium and Cooperative Apartment [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans		73,557	61,256
Real Estate Loan [Member] | One- to Four-Family Residential, Including Condominium and Cooperative Apartment [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans		214	945
Real Estate Loan [Member] | One- to Four-Family Residential, Including Condominium and Cooperative Apartment [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans		1,526	2,196
Real Estate Loan [Member] | One- to Four-Family Residential, Including Condominium and Cooperative Apartment [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans		0	0
Real Estate Loan [Member] | Multifamily Residential and Residential Mixed Use [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans		4,458,146	3,759,907
Real Estate Loan [Member] | Multifamily Residential and Residential Mixed Use [Member] | Not Graded [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans	[1]		0
Real Estate Loan [Member] | Multifamily Residential and Residential Mixed Use [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans		4,447,110	3,743,298
Real Estate Loan [Member] | Multifamily Residential and Residential Mixed Use [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans		3,785	9,759
Real Estate Loan [Member] | Multifamily Residential and Residential Mixed Use [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans		7,251	6,850
Real Estate Loan [Member] | Multifamily Residential and Residential Mixed Use [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans		0	0
Real Estate Loan [Member] | Commercial Mixed Use Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans		402,709	377,275
Real Estate Loan [Member] | Commercial Mixed Use Real Estate [Member] | Not Graded [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans	[1]		0
Real Estate Loan [Member] | Commercial Mixed Use Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans		395,070	370,110
Real Estate Loan [Member] | Commercial Mixed Use Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans		2,133	1,622
Real Estate Loan [Member] | Commercial Mixed Use Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans		5,506	5,543
Real Estate Loan [Member] | Commercial Mixed Use Real Estate [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans		0	0
Real Estate Loan [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans		552,339	485,909
Real Estate Loan [Member] | Commercial Real Estate [Member] | Not Graded [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans	[1]		0
Real Estate Loan [Member] | Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans		544,551	473,242
Real Estate Loan [Member] | Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans		528	4,857
Real Estate Loan [Member] | Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans		7,260	7,810
Real Estate Loan [Member] | Commercial Real Estate [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total real estate loans		0	0
Consumer Loans [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total consumer loans		1,673	1,586
Consumer Loans [Member] | Non-Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Total consumer loans		$ 2	$ 4

[1] Amount comprised of fully performing one- to four-family residential and condominium and cooperative unit loans with balances equal to or less than the FNMA Limits.