Loans Receivable, Net - Overall Statistics for Loans Receivable Portfolio (Parenthetical) (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Floating rate loans		$ 216.3
Average floor rate		1.27%
Percentage of loans subject to yield maintenance, or other prepayment restrictions	75.00%	64.00%
Percentage of loans open to repayment by borrower without penalty	25.00%	36.00%
USD LIBOR [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of loans receivable by type	92.00%	84.00%