Loans Receivable - Allocation of Loans Receivable by Loan Type and Internal Risk Ratings (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014 SecurityLoan	Dec. 31, 2013 SecurityLoan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	$ 2,710,159	$ 2,047,223
Senior Mortgages Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans	36	26
Principal Balance	2,478,840	1,811,513
Net book value	2,461,832	1,800,329
Senior Mortgages Loans [Member] | Risk Rating 1-3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans	36	26
Principal Balance	2,478,840	1,811,513
Net book value	2,461,832	1,800,329
Senior Mortgages Loans [Member] | Risk Rating 4-5 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans
Principal Balance
Net book value
Senior Mortgages Loans [Member] | Risk Rating 6-8 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans
Principal Balance
Net book value
Subordinate Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans	5	5
Principal Balance	264,957	264,898
Net book value	248,327	246,894
Subordinate Loans [Member] | Risk Rating 1-3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans	3	3
Principal Balance	227,409	227,350
Net book value	221,327	219,894
Subordinate Loans [Member] | Risk Rating 4-5 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans
Principal Balance
Net book value
Subordinate Loans [Member] | Risk Rating 6-8 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans	2	2
Principal Balance	37,548	37,548
Net book value	$ 27,000	$ 27,000