Summary of Significant Accounting Policies - Investments, Derivatives, Commercial Loan Investment Impairment, Accounts Receivable, and Land and Development Costs (Details)	12 Months Ended
	Dec. 31, 2016 USD ($) derivative	Dec. 31, 2015 USD ($) derivative item	Dec. 31, 2014 USD ($)
Description of Business [Line Items]
Impairment charge other-than-temporary impairments	$ 0	$ 60,000	$ 0
Realized Loss (Gain) on Investment Securities	$ 575,567	$ (163,189)	$ (4,835)
Derivatives outstanding | derivative	0	0
Allowance for impairment of loans	$ 0	$ 0
Allowance for doubtful accounts	0	0
Tenant Reimbursable Expenses
Description of Business [Line Items]
Accounts receivable included in other assets	125,000	831,000
Real Estate Operations
Description of Business [Line Items]
Accounts receivable included in other assets	3,800,000	$ 1,300,000
Number of separate land transactions | item		2
ship And Event Receivables
Description of Business [Line Items]
Accounts receivable included in other assets	$ 326,000	$ 253,000