| 
           Accrued Interest Receivable Schedule of Accounts, Notes, Loans and Financing Receivable (Details) (USD $) 
        In Thousands, unless otherwise specified  | 
        
           Jun. 30, 2012 
         | 
        
           Dec. 31, 2011 
         | 
      
|---|---|---|
| Accounts, Notes, Loans and Financing Receivable [Line Items] | ||
| Interest Receivable | $ 35,954 | $ 23,437 | 
| 
           Loans Held-for-sale, Mortgages [Member] 
         | 
        ||
| Accounts, Notes, Loans and Financing Receivable [Line Items] | ||
| Interest Receivable | 79 | 38 | 
| 
           US Treasury Securities [Member] 
         | 
        ||
| Accounts, Notes, Loans and Financing Receivable [Line Items] | ||
| Interest Receivable | 1,101 | 1,003 | 
| 
           Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member] 
         | 
        ||
| Accounts, Notes, Loans and Financing Receivable [Line Items] | ||
| Interest Receivable | 9,089 | 5,844 | 
| 
           Federal National Mortgage Association Certificates and Obligations (FNMA) [Member] 
         | 
        ||
| Accounts, Notes, Loans and Financing Receivable [Line Items] | ||
| Interest Receivable | 16,049 | 9,770 | 
| 
           Government National Mortgage Association Certificates and Obligations (GNMA) [Member] 
         | 
        ||
| Accounts, Notes, Loans and Financing Receivable [Line Items] | ||
| Interest Receivable | 6,869 | 4,454 | 
| 
           Mortgage-backed Securities, Issued by Private Enterprises [Member] 
         | 
        ||
| Accounts, Notes, Loans and Financing Receivable [Line Items] | ||
| Interest Receivable | 2,767 | 2,328 | 
| 
           Available-for-sale Securities [Member] 
         | 
        ||
| Accounts, Notes, Loans and Financing Receivable [Line Items] | ||
| Interest Receivable | $ 34,774 | $ 22,396 |