LOANS RECEIVABLE AND CREDIT QUALITY, Credit Quality Indicators (Details) - USD ($) $ in Thousands		Jun. 30, 2015	Dec. 31, 2014
One-to four Family Residential and Cooperative Unit [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Not Individually Assigned Credit Rating	[1]	$ 8,008	$ 9,091
Financing Receivable, Net		70,875	73,500
Multifamily Residential and Residential Mixed Use [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Not Individually Assigned Credit Rating	[1]	0	0
Financing Receivable, Net		3,433,552	3,298,448
Mixed Use Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Not Individually Assigned Credit Rating	[1]	0	0
Financing Receivable, Net		357,988	328,667
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Not Individually Assigned Credit Rating	[1]	0	0
Financing Receivable, Net		441,894	416,796
Construction Loan Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Not Individually Assigned Credit Rating	[1]	0	0
Financing Receivable, Net		0	0
Consumer Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Not Individually Assigned Credit Rating		1,954	1,829
Total Real Estate Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Not Individually Assigned Credit Rating	[1]	8,008	9,091
Financing Receivable, Net		4,304,309	4,117,411
Pass [Member] | One-to four Family Residential and Cooperative Unit [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Not Individually Assigned Credit Rating		59,639	60,764
Pass [Member] | Multifamily Residential and Residential Mixed Use [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Not Individually Assigned Credit Rating		3,419,617	3,271,430
Pass [Member] | Mixed Use Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Not Individually Assigned Credit Rating		350,247	317,718
Pass [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Not Individually Assigned Credit Rating		426,999	391,227
Pass [Member] | Construction Loan Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Not Individually Assigned Credit Rating		0	0
Pass [Member] | Consumer Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Not Individually Assigned Credit Rating		1,951	1,825
Pass [Member] | Total Real Estate Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Not Individually Assigned Credit Rating		4,256,502	4,041,139
Special Mention [Member] | One-to four Family Residential and Cooperative Unit [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Individually Assigned Credit Rating		1,354	1,370
Special Mention [Member] | Multifamily Residential and Residential Mixed Use [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Individually Assigned Credit Rating		8,441	20,738
Special Mention [Member] | Mixed Use Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Individually Assigned Credit Rating		2,550	4,944
Special Mention [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Individually Assigned Credit Rating		5,893	6,431
Special Mention [Member] | Construction Loan Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Individually Assigned Credit Rating		0	0
Special Mention [Member] | Total Real Estate Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Individually Assigned Credit Rating		18,238	33,483
Substandard [Member] | One-to four Family Residential and Cooperative Unit [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Individually Assigned Credit Rating		1,874	2,275
Substandard [Member] | Multifamily Residential and Residential Mixed Use [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Individually Assigned Credit Rating		5,494	6,280
Substandard [Member] | Mixed Use Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Individually Assigned Credit Rating		5,191	6,005
Substandard [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Individually Assigned Credit Rating		9,002	19,138
Substandard [Member] | Construction Loan Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Individually Assigned Credit Rating		0	0
Substandard [Member] | Total Real Estate Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Individually Assigned Credit Rating		21,561	33,698
Doubtful [Member] | One-to four Family Residential and Cooperative Unit [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Individually Assigned Credit Rating		0	0
Doubtful [Member] | Multifamily Residential and Residential Mixed Use [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Individually Assigned Credit Rating		0	0
Doubtful [Member] | Mixed Use Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Individually Assigned Credit Rating		0	0
Doubtful [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Individually Assigned Credit Rating		0	0
Doubtful [Member] | Construction Loan Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Individually Assigned Credit Rating		0	0
Doubtful [Member] | Total Real Estate Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Individually Assigned Credit Rating		0	0
Non Accrual Financing Receivable [Member] | Consumer Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Not Individually Assigned Credit Rating		$ 3	$ 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.