Variable Interest Entities - Summary of Geographic Concentrations of Residential Mortgage Loans Held-for-Investment (Parenthetical) (Detail)	3 Months Ended	12 Months Ended
Mar. 31, 2016	Dec. 31, 2015
Variable Interest Entities Primary Beneficiary \| Geographic Concentration Risk \| Residential Loans Held For Investment
Concentration Risk [Line Items]
Concentration risk percentage on other state	5.00%	5.00%

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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