Loans Held for Investment and Allowance for Loan Losses - (Credit Risk Profile, Narrative) (Detail)	3 Months Ended
	Mar. 31, 2016 Score
Maximum | Loans (1 Rated)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan-to-value ratio	65.00%
Maximum | Loans (2 Rated)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan-to-value ratio	75.00%
Maximum | Loans (4 Rated)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cash flow coverage	1.00
Minimum | Loans (1 Rated)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Debt service coverage	1.75
Discounted collateral coverage	125.00%
Credit score	740
Minimum | Loans (3 Rated)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Debt service coverage	1.00
Minimum | Loans (2 Rated)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Debt service coverage	1.25
Discounted collateral coverage	100.00%
Credit score	700