Loans Receivable - Allocation of Loans Receivable by Both Loan Type and Internal Risk Ratings (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013 SecurityLoan	Dec. 31, 2012 SecurityLoan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Book Value, net	$ 830,101	$ 141,500
Subordinated Interests in Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans	5	6
Principal Balance	95,079	101,680
Book Value, net	77,000	79,000
Subordinated Interests in Mortgages [Member] | Risk Rating 1-3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans	1	2
Principal Balance	20,000	47,000
Book Value, net	20,000	47,000
Subordinated Interests in Mortgages [Member] | Risk Rating 4-5 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans	2	1
Principal Balance	57,000	30,000
Book Value, net	57,000	30,000
Subordinated Interests in Mortgages [Member] | Risk Rating 6-8 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans	2	3
Principal Balance	18,079	24,680
Book Value, net		2,000
Senior Mortgages Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans	8	1
Principal Balance	756,638	62,500
Book Value, net	753,101	62,500
Senior Mortgages Loans [Member] | Risk Rating 1-3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans	8
Principal Balance	756,638
Book Value, net	753,101
Senior Mortgages Loans [Member] | Risk Rating 4-5 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans		1
Principal Balance		62,500
Book Value, net		$ 62,500