Stockholders' Equity - Schedule of the Components of Non-controlling Interests (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Gross investment in CT Legacy Partners:
Restricted cash	$ 21,972	$ 14,246
Loans receivable, at fair value	117,549
Accrued interest receivable, prepaid expenses, and other assets	30,697	5,868
Accounts payable, accrued expenses and other liabilities	36,879	21,209
Non-controlling interests in CT Legacy Partners	88,978	80,009
Noncontrolling Interests [Member]
Gross investment in CT Legacy Partners:
Restricted cash	21,972
Loans receivable, at fair value	117,549
Accrued interest receivable, prepaid expenses, and other assets	21,948
Accounts payable, accrued expenses and other liabilities	(485)
Investment in CT Legacy REIT, Gross	160,984
Equity interests owned by Blackstone Mortgage Trust, Inc.	(72,006)
Non-controlling interests in CT Legacy Partners	$ 88,978