Loans Receivable - Types of Loans in Loan Portfolio, as well as Property Type and Geographic Distribution of Properties Securing these Loans (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	$ 2,047,223	$ 141,500
Senior Mortgages Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	1,800,329	62,500
Percentage of Book Value	88.00%	44.00%
Subordinate Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	246,894	79,000
Percentage of Book Value	12.00%	56.00%
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	2,047,223	141,500
Loans Receivable [Member] | Asset [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	2,047,223	141,500
Percentage of Book Value	100.00%	100.00%
Office [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	864,666	111,500
Percentage of Book Value	42.00%	79.00%
Multifamily [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	617,464
Percentage of Book Value	30.00%
Hotel [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	390,492	30,000
Percentage of Book Value	19.00%	21.00%
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	174,601
Percentage of Book Value	9.00%
Northeast [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	828,571	27,000
Percentage of Book Value	40.00%	19.00%
West [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	469,262	92,500
Percentage of Book Value	23.00%	65.00%
Southeast [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	243,798	12,404
Percentage of Book Value	12.00%	9.00%
Southwest [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	216,429	9,596
Percentage of Book Value	11.00%	7.00%
Northwest [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	166,207
Percentage of Book Value	8.00%
Midwest [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	85,708
Percentage of Book Value	4.00%
United Kingdom [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	$ 37,248
Percentage of Book Value	2.00%