Loans Receivable and Allowance for Loan Losses (Details 9) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Balances of multi-family and commercial real estate mortgage loan receivable segments by credit quality indicator
Total	$ 13,155,914	$ 13,197,560
Mortgage Loans (Gross)
Balances of multi-family and commercial real estate mortgage loan receivable segments by credit quality indicator
Total	12,891,820	12,915,116
Mortgage Loans (Gross) | Multi-Family
Balances of multi-family and commercial real estate mortgage loan receivable segments by credit quality indicator
Total	2,406,678	1,693,871
Mortgage Loans (Gross) | Multi-Family | Not criticized
Balances of multi-family and commercial real estate mortgage loan receivable segments by credit quality indicator
Total	2,271,006	1,557,315
Mortgage Loans (Gross) | Multi-Family | Criticized
Balances of multi-family and commercial real estate mortgage loan receivable segments by credit quality indicator
Total	135,672	136,556
Mortgage Loans (Gross) | Commercial Real Estate
Balances of multi-family and commercial real estate mortgage loan receivable segments by credit quality indicator
Total	773,916	659,706
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	706,334	596,799
Mortgage Loans (Gross) | Commercial Real Estate | Criticized
Balances of multi-family and commercial real estate mortgage loan receivable segments by credit quality indicator
Total	$ 67,582	$ 62,907