Description of Business and Principles of Interim Statements - Additional Information (Detail)	3 Months Ended			12 Months Ended
	Mar. 31, 2016 USD ($) ft² a State Property Billboard Loan	Dec. 31, 2015 USD ($) a	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($) a	Feb. 18, 2016 a	Dec. 31, 2013 USD ($)	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	32
Self developed multi-tenant properties | Property	9
Gross leasable space	1,700,000	160		160	0.37
Land portfolio | a	10,500
Number of billboards leased for property | Billboard	20
Cash and cash equivalents maximum original maturity period	90 days
Restricted Cash	$ 15,156,505	$ 14,060,523		$ 14,060,523
Cash held in reserve for property taxes and insurance escrows	13,600,000
Cash held in escrow related to land transaction	219,000					$ 4,000
Number of income properties acquired | Property							2
Reserve for future interest payment	751,000
Impairment charge other-than-temporary impairments	0	60,000	$ 0	60,000
Net realized loss on investments	(575,567)		$ 130,791
Allowance for doubtful accounts	0	0		0
Amount reclassified from other assets to long-term debt		1,700,000		1,700,000
Tenant Reimbursable Expenses
Description of Business [Line Items]
Accounts receivable included in other assets	295,000	831,000		831,000
Real Estate Operations
Description of Business [Line Items]
Accounts receivable included in other assets	2,800,000	1,300,000		1,300,000
ship And Event Receivables
Description of Business [Line Items]
Accounts receivable included in other assets	$ 435,000	$ 253,000		$ 253,000
Atlanta, GA [Member]
Description of Business [Line Items]
Number of commercial mortgage loan investments | Loan	4
Katy, Texas [Member] | Reserve for Tenant Improvements [Member]
Description of Business [Line Items]
Restricted Cash	$ 626,000