Loans Receivable - Allocates Net Book Value and Principal Balance of Loans Receivable Based on 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
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans	13	7
Principal Balance	851,716	164,180
Book Value, net	830,101	141,500
Risk Rating 1-3 [Member] | Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans	9	2
Principal Balance	776,637	47,000
Book Value, net	773,101	47,000
Risk Rating 4-5 [Member] | Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans	2	2
Principal Balance	57,000	92,500
Book Value, net	57,000	92,500
Risk Rating 6-8 [Member] | Loans Receivable [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