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Commercial Mortgage Loans - Commercial Mortgage Loan Portfolio (Parenthetical) (Detail) (USD $) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2012 | Mar. 31, 2013
Mixed Use [Member] | Massachusetts [Member] |  |
Mortgage Loans on Real Estate [Line Items] |  |
Senior sub-participation interest in New York, NY Hotel Loan | $ 120,000 | $ 120,000
Repayment of first mortgage | $ 33,000 |
Condo Conversion [Member] |  |
Mortgage Loans on Real Estate [Line Items] |  |
Extension options | Two one-year | Two one-year
Condo Conversion [Member] | New York [Member] |  |
Mortgage Loans on Real Estate [Line Items] |  |
Extension options | Two one-year | Two one-year

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- Details
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