Fair Value Measurement - Additional Information (Detail) - Level 3 - Loans Held for Investment - Appraisal Value	Sep. 30, 2017	Dec. 31, 2016
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-recoverable rate	0.00%	0.00%
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-recoverable rate	17.00%	73.00%
Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-recoverable rate	12.00%	16.00%