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	Jun. 30, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	$ 3,488,179	$ 2,047,223
Senior Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	3,285,398	1,800,329
Percentage of Book Value	94.00%	88.00%
Subordinate Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	202,781	246,894
Percentage of Book Value	6.00%	12.00%
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	3,488,179	2,047,223
Percentage of Book Value	100.00%	100.00%
Office [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	1,296,464	864,666
Percentage of Book Value	37.00%	42.00%
Hotel [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	1,117,724	390,492
Percentage of Book Value	32.00%	19.00%
Multifamily [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	451,193	341,819
Percentage of Book Value	13.00%	17.00%
Condominium [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	317,876	275,645
Percentage of Book Value	9.00%	13.00%
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	304,922	174,601
Percentage of Book Value	9.00%	9.00%
United States Northeast [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	1,149,246	828,571
Percentage of Book Value	33.00%	40.00%
United States West [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	708,564	469,262
Percentage of Book Value	20.00%	23.00%
United States Southeast [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	437,627	243,798
Percentage of Book Value	12.00%	12.00%
United States Southwest [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	304,747	216,429
Percentage of Book Value	9.00%	11.00%
United States Northwest [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	240,685	166,207
Percentage of Book Value	7.00%	8.00%
United States Midwest [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	100,865	85,708
Percentage of Book Value	3.00%	4.00%
United States [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	2,941,734	2,009,975
Percentage of Book Value	84.00%	98.00%
United Kingdom [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	508,872	37,248
Percentage of Book Value	15.00%	2.00%
Netherlands [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	37,573
Percentage of Book Value	1.00%
International [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	$ 546,445	$ 37,248
Percentage of Book Value	16.00%	2.00%