Loans Receivable - Overall Statistics for Loans Receivable Portfolio (Parenthetical) (Detail) - USD ($) $ in Billions	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commitments expiration period	4 years
Percentage of loans receivable by type		14.00%
Floating rate loans	$ 1.1
Average floor rate	0.64%	0.31%
Percentage of loans subject to yield maintenance, or other prepayment restrictions	65.00%	85.00%
Percentage of loans open to repayment by borrower without penalty	35.00%	15.00%
USD LIBOR [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of loans receivable by type	84.00%	79.00%
Unfunded Commitments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commitments expiration period	4 years	4 years