Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Significant Accounting Policies [Line Items]
Reclassification from property income to real estate operating expenses		$ 695,000
Real estate operating expense	$ 30,706,000	25,277,000
Depreciation and amortization expense	24,276,000	19,024,000
Federal deposit insurance corporation, insurance limit per institution	250,000
Restricted cash	200,166,000		$ 213,012,000
Accrued interest receivable	49,987,000		47,343,000
Earned asset management fees	402,000	315,000
Investment in securities	0		0
Investments in securities sold during the period		31,412,000
Intangible assets, accumulated amortization	32,228,000		26,307,000
Intangible assets, amortization expenses	5,920,000	3,931,000
Expected amortization expense of intangible assets, remainder of 2016	5,141,000
Expected amortization expense of intangible assets in 2017	4,861,000
Expected amortization expense of intangible assets in 2018	3,662,000
Expected amortization expense of intangible assets in 2019	3,209,000
Expected amortization expense of intangible assets in 2020	2,764,000
Expected amortization expense of intangible assets thereafter	7,062,000
Goodwill	8,854,000		8,854,000
Deferred Costs, Net			31,368,000
Deferred financing costs, accumulated amortization			33,769,000
Customer relationships
Significant Accounting Policies [Line Items]
Intangible assets, gross carrying amount	19,149,000		19,149,000
In-place leases
Significant Accounting Policies [Line Items]
Intangible assets, gross carrying amount	38,277,000		38,333,000
Trade name
Significant Accounting Policies [Line Items]
Intangible assets, gross carrying amount	1,500,000		1,500,000
IRT
Significant Accounting Policies [Line Items]
Earned asset management fees	1,631,000	1,001,000
Incentive fees	65,000	211,000
Property management and leasing fees	1,262,000	755,000
Loans and Finance Receivables
Significant Accounting Policies [Line Items]
Accrued interest receivable	35,977,000		34,132,000
Impairment of loans	$ 0		0
Building and Building Improvements | Minimum
Significant Accounting Policies [Line Items]
Property, useful lives	30 years
Building and Building Improvements | Maximum
Significant Accounting Policies [Line Items]
Property, useful lives	40 years
Furniture, fixtures, and equipment | Minimum
Significant Accounting Policies [Line Items]
Property, useful lives	5 years
Furniture, fixtures, and equipment | Maximum
Significant Accounting Policies [Line Items]
Property, useful lives	10 years
Tenant escrows and borrowers' funds
Significant Accounting Policies [Line Items]
Restricted cash	$ 158,177,000		165,866,000
Securitizations
Significant Accounting Policies [Line Items]
Restricted cash	$ 41,989,000		$ 47,146,000
Cash and Cash Equivalents
Significant Accounting Policies [Line Items]
Increase (decrease) in cash flows activities		0
Cash Flows from Operating Activities
Significant Accounting Policies [Line Items]
Increase (decrease) in cash flows activities		(18,194,000)
Cash Flows from Investing Activities
Significant Accounting Policies [Line Items]
Increase (decrease) in cash flows activities		18,194,000
Scenario, Adjustment
Significant Accounting Policies [Line Items]
Real estate operating expense		702,000
Depreciation and amortization expense		$ 7,000