Loans Receivable and Allowance for Loan Losses (Multi-Family and Commercial Real Estate Loans, by Credit Quality Indicator) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Balances of multi-family and commercial real estate mortgage loan receivable segments by credit quality indicator
Total	$ 11,866,764	$ 12,386,378
Mortgage loans (gross)
Balances of multi-family and commercial real estate mortgage loan receivable segments by credit quality indicator
Total	11,621,768	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	3,659,236	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	3,604,937	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	22,390	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	31,157	72,606
Mortgage loans (gross) | Multi-family | Doubtful
Balances of multi-family and commercial real estate mortgage loan receivable segments by credit quality indicator
Total	752
Mortgage loans (gross) | Commercial real estate
Balances of multi-family and commercial real estate mortgage loan receivable segments by credit quality indicator
Total	880,308	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	825,089	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	16,578	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	$ 38,641	$ 44,092