Loans and Allowance for Loan Losses (Details Textual) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Mortgage Loans on Real Estate [Line Items]
Total loans	$ 30,073,320,000		$ 30,073,320,000		$ 30,606,270,000
Principal balance of loans with payment plans	27,900,000		27,900,000		81,300,000
Loans modified in a troubled debt restructuring	41,800,000		41,800,000		11,100,000
Description related to classification of major category and sub categories of loans held			We evaluate the classification of our one-to four- family mortgage loans, consumer loans and other loans primarily on a pooled basis by delinquency. Loans that are past due 60 to 89 days are classified as special mention and loans that are past due 90 days or more are classified as substandard. We generally obtain updated valuations for one- to four- family mortgage loans by the time a loan becomes 180 days past due.
Percentage of total loans within the New York metropolitan area	79.90%		79.90%		78.40%
Initial terms of interest-only loans originating as adjustable-rate mortgage loans			5, 7 or 10 years
Loans eligible for limited documentation processing			ARM loans, interest-only first mortgage loans and 10-, 15-, 20-, 30- and 40-year fixed-rate loans to owner-occupied primary and second home applicants
Term (in years) of interest-only loans offered as fixed-rate loans			30
Number of years with interest-only payments for interest-only loans offered as fixed-rate loans			10
Non-performing interest-only loans	192,300,000		192,300,000		179,300,000
Maximum percentage of borrowings available under limited documentation loans			70% of the lower of the appraised value or purchase price of the property
Maximum loan amount for limited documentation loans			750,000
Maximum loan-to-value ratio for mortgage loans with no verification of income			60.00%
Originated amortizing limited documentation loans	3,700,000,000		3,700,000,000		3,380,000,000
Originated limited documentation interest-only loans	971,800,000		971,800,000		938,800,000
Non-performing loans originated amortizing limited documentation loans	112,400,000		112,400,000		91,500,000
Non-performing loans originated limited documentation interest-only loans	62,600,000		62,600,000		58,300,000
Charge-offs resulting from impairment evaluation			875,000
ALL established for loans classified as troubled debt restructurings			4,900,000
Net charge-offs	22,977,000	22,846,000	44,268,000	47,091,000
Previous charges-offs on Real Estate owned			8,200,000
Number of loans disposed through foreclosure process			74
Final gain on sale of loans disposed through foreclosure process			822,000
Write-downs on foreclosed real estate			3,700,000
Percentage of average LTV ratio of non-performing loans	74.90%		74.90%
Percentage of average LTV ratio of total mortgage loan portfolio	60.80%		60.80%
Percentage of non-performing loans within the New York metropolitan area	72.70%		72.70%		70.90%
Percentage of weighted average LTV in the one- to four-family mortgage loan portfolio	60.80%		60.80%
Number of delinquency days before new collateral values for loans are obtained			0
Percentage decline of house prices in the New York metropolitan area (locally) from the peak of the market in 2006	23.00%		23.00%
Percentage decline of house prices (nationwide) from the peak of the market in 2006	32.00%		32.00%
Interest income on non-accrual loans that would have been recognized if interest had been recorded based upon original contract terms			26,100,000
Loans held for sale	0		0		0
Period in which loans are considered contractually past due			90 days or more
One- to four-family, Interest-only [Member]
Mortgage Loans on Real Estate [Line Items]
Total loans	5,065,540,000		5,065,540,000		5,136,463,000
Current Dues [Member]
Mortgage Loans on Real Estate [Line Items]
Principal balance of loans with payment plans	20,500,000		20,500,000		54,400,000
Thirty To Fifty Nine Days Past Due [Member]
Mortgage Loans on Real Estate [Line Items]
Principal balance of loans with payment plans	2,500,000		2,500,000		13,900,000
Sixty To Eighty Nine Days Past Due [Member]
Mortgage Loans on Real Estate [Line Items]
Principal balance of loans with payment plans	2,900,000		2,900,000		4,700,000
Loans modified in a troubled debt restructuring	1,800,000		1,800,000
Ninety Days Or More Past Due [Member]
Mortgage Loans on Real Estate [Line Items]
Principal balance of loans with payment plans	2,000,000		2,000,000		8,300,000
Loans modified in a troubled debt restructuring	2,600,000		2,600,000
Thirty Days Past Due [Member]
Mortgage Loans on Real Estate [Line Items]
Loans modified in a troubled debt restructuring	$ 1,900,000		$ 1,900,000