Loans Receivable - Overall Statistics for Loan Receivables Portfolio (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013 Investment	Dec. 31, 2012 Investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	$ 1,362,891	$ 141,500
Weighted-average cash coupon	L+1.60 %
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans	22	7
Principal Balance	1,387,067	164,180
Net book value	$ 1,362,891	$ 141,500
Weighted-average cash coupon	L+4.28 %	L+2.51 %
Weighted-average all-in yield	L+4.91 %	L+4.53 %
Weighted-average maximum maturity (years)	4 years	8 months 12 days