LOANS RECEIVABLE AND CREDIT QUALITY, Credit Quality Indicators (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 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	$ 8,499	[1]	$ 9,091	[1]
Financing Receivable, Net	70,982		73,500
Multifamily Residential and Residential Mixed Use [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Not Individually Assigned Credit Rating	0	[1]	0	[1]
Financing Receivable, Net	3,398,532		3,298,448
Mixed Use Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Not Individually Assigned Credit Rating	0	[1]	0	[1]
Financing Receivable, Net	335,417		328,667
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Not Individually Assigned Credit Rating	0	[1]	0	[1]
Financing Receivable, Net	428,174		416,796
Construction Loan Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Not Individually Assigned Credit Rating	0	[1]	0	[1]
Financing Receivable, Net	0		0
Consumer Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Not Individually Assigned Credit Rating	1,612		1,829
Total Real Estate Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Not Individually Assigned Credit Rating	8,499	[1]	9,091	[1]
Financing Receivable, Net	4,233,105		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	59,088		60,764
Pass [Member] | Multifamily Residential and Residential Mixed Use [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Not Individually Assigned Credit Rating	3,373,334		3,271,430
Pass [Member] | Mixed Use Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Not Individually Assigned Credit Rating	327,641		317,718
Pass [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Not Individually Assigned Credit Rating	408,437		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	1,608		1,825
Pass [Member] | Total Real Estate Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Not Individually Assigned Credit Rating	4,168,500		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	1,362		1,370
Special Mention [Member] | Multifamily Residential and Residential Mixed Use [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Individually Assigned Credit Rating	19,043		20,738
Special Mention [Member] | Mixed Use Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Individually Assigned Credit Rating	3,242		4,944
Special Mention [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Individually Assigned Credit Rating	6,164		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	29,811		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	2,033		2,275
Substandard [Member] | Multifamily Residential and Residential Mixed Use [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Individually Assigned Credit Rating	6,155		6,280
Substandard [Member] | Mixed Use Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Individually Assigned Credit Rating	4,534		6,005
Substandard [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Individually Assigned Credit Rating	13,573		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	26,295		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	$ 4		$ 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.