Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Jun. 30, 2016 USD ($) Customer	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Significant Accounting Policies [Line Items]
Reclassification from property income to fee and other income and to real estate operating expense			$ 61,000			$ 634,000
Depreciation and amortization expense	$ 22,806,000		17,007,000		$ 47,082,000	36,031,000
Fee and other income	2,775,000		7,629,000		5,627,000	13,223,000
Real estate operating expense	29,950,000		26,630,000		60,656,000	51,907,000
Investment interest expense	9,125,000		7,582,000		18,445,000	14,496,000
Federal deposit insurance corporation, insurance limit per institution	250,000				250,000
Restricted cash	159,429,000				159,429,000		$ 213,012,000
Accrued interest receivable	42,139,000				42,139,000		47,343,000
Earned asset management fees	376,000		743,000		778,000	1,058,000
Investment in securities	0				0		0
Investments in securities sold during the period				$ 31,412,000
Intangible assets, accumulated amortization	34,876,000				34,876,000		26,307,000
Intangible assets, amortization expenses	5,468,000		3,299,000		11,584,000	7,409,000
Expected amortization expense of intangible assets, remainder of 2016	4,694,000				4,694,000
Expected amortization expense of intangible assets in 2017	5,541,000				5,541,000
Expected amortization expense of intangible assets in 2018	4,198,000				4,198,000
Expected amortization expense of intangible assets in 2019	3,600,000				3,600,000
Expected amortization expense of intangible assets in 2020	3,022,000				3,022,000
Expected amortization expense of intangible assets thereafter	7,145,000				7,145,000
Goodwill	8,854,000				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	14,997,000				14,997,000		19,149,000
Intangible assets, gross carrying amount, decreased	(4,151,000)
Intangible assets, accelerated amortization					$ 2,552,000
Number of cancelled customer relationships | Customer					2
In-place leases
Significant Accounting Policies [Line Items]
Intangible assets, gross carrying amount	42,443,000				$ 42,443,000		38,333,000
Trade name
Significant Accounting Policies [Line Items]
Intangible assets, gross carrying amount	1,500,000				1,500,000		1,500,000
IRT
Significant Accounting Policies [Line Items]
Earned asset management fees	1,783,000		1,046,000		3,414,000	2,047,000
Incentive fees	79,000		214,000		144,000	437,000
Property management and leasing fees	1,229,000		764,000		2,491,000	1,519,000
Loans and Finance Receivables
Significant Accounting Policies [Line Items]
Accrued interest receivable	28,358,000				28,358,000		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	144,947,000				$ 144,947,000		165,866,000
Securitizations
Significant Accounting Policies [Line Items]
Restricted cash	14,482,000				14,482,000		$ 47,146,000
Subsidiaries
Significant Accounting Policies [Line Items]
Write off of retail property investment	$ 864,000				864,000
Cash and Cash Equivalents
Significant Accounting Policies [Line Items]
Increase (decrease) in cash flows activities				0		0
Impact on Investment Interest Expense by Increasing Investment Interest Expense and Decreasing Interest Expense
Significant Accounting Policies [Line Items]
Investment interest expense		$ 1,424
Cash Flows from Operating Activities
Significant Accounting Policies [Line Items]
Increase (decrease) in cash flows activities				(18,194,000)	(69,028,000)
Cash Flows from Investing Activities
Significant Accounting Policies [Line Items]
Increase (decrease) in cash flows activities				$ 18,194,000	$ 69,028,000
Scenario, Adjustment
Significant Accounting Policies [Line Items]
Depreciation and amortization expense			2,000			9,000
Fee and other income			214,000			214,000
Real estate operating expense			$ (275,000)			$ 420,000