Fair Value of Financial Instruments - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Dealer marks of securities	74.00%
Percentage difference of internal valuation than dealer marks	5.00%
Residential | Senior Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	22,000
Residential | Subordinate Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	27
Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Dealer marks of securities	95.00%
Percentage difference of internal valuation than dealer marks	4.00%