Loans Receivable and Allowance for Loan Losses (Details 6) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Balances of multi-family and commercial real estate mortgage loan receivable segments by credit quality indicator
Total	$ 12,009,959	$ 12,386,378
Mortgage Loans (Gross)
Balances of multi-family and commercial real estate mortgage loan receivable segments by credit quality indicator
Total	11,770,730	12,146,697
Mortgage Loans (Gross) | Multi-Family
Balances of multi-family and commercial real estate mortgage loan receivable segments by credit quality indicator
Total	3,583,608	3,296,455
Mortgage Loans (Gross) | Multi-Family | Not criticized
Balances of multi-family and commercial real estate mortgage loan receivable segments by credit quality indicator
Total	3,526,105	3,209,786
Mortgage Loans (Gross) | Multi-Family | Special mention
Balances of multi-family and commercial real estate mortgage loan receivable segments by credit quality indicator
Total	17,261	14,063
Mortgage Loans (Gross) | Multi-Family | Substandard
Balances of multi-family and commercial real estate mortgage loan receivable segments by credit quality indicator
Total	40,242	72,606
Mortgage Loans (Gross) | Commercial Real Estate
Balances of multi-family and commercial real estate mortgage loan receivable segments by credit quality indicator
Total	862,448	812,966
Mortgage Loans (Gross) | Commercial Real Estate | Not criticized
Balances of multi-family and commercial real estate mortgage loan receivable segments by credit quality indicator
Total	816,216	759,114
Mortgage Loans (Gross) | Commercial Real Estate | Special mention
Balances of multi-family and commercial real estate mortgage loan receivable segments by credit quality indicator
Total	9,937	9,760
Mortgage Loans (Gross) | Commercial Real Estate | Substandard
Balances of multi-family and commercial real estate mortgage loan receivable segments by credit quality indicator
Total	$ 36,295	$ 44,092