Description of Business and Principles of Interim Statements - Additional Information (Detail)	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) ft² a State Property Billboard Loan	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) Property Derivative	Jan. 31, 2013 Property
Description of Business [Line Items]
Number of states in which entity operates | State		10
Number of owned and managed commercial real estate properties | Property		41
Commercial real estate properties | Property		33
Self developed multi-tenant properties | Property		8
Gross leasable space | ft²		1,270,000
Land portfolio | a		10,500
Number of billboards leased for property | Billboard		21
Restricted Cash		$ 10,625,517		$ 4,440,098
Proceeds from sale of income property		9,000,000
Cash held in escrow related to land transaction		285,000
Cash held in reserve for property taxes and insurance escrows		$ 431,000
Number of income properties acquired | Property		3		3	2
Derivatives outstanding | Derivative				0
Amount reclassified to land, timber, and development costs				$ 14,900,000
Reclassifications to the purchase price allocations, increase in intangible assets				3,000,000
Reclassifications to the purchase price allocations, decrease in properties, land, buildings, and improvements				(2,300,000)
Reclassifications to the purchase price allocations, increase in accrued and other liabilities				$ 670,000
Increase in revenues and the direct costs of revenues	$ 137,000		$ 259,000
Atlanta, GA [Member]
Description of Business [Line Items]
Number of commercial mortgage loan investments | Loan		4
Katy, Texas [Member]
Description of Business [Line Items]
Cash held in escrow related to land transaction		$ 276,000
Katy, Texas [Member] | Tenant Improvements [Member]
Description of Business [Line Items]
Restricted Cash		$ 596,000