Unsecured Lines of Credit - Summary of Unsecured Lines of Credit (Details) - USD ($)		9 Months Ended	12 Months Ended
		Sep. 30, 2019	Dec. 31, 2018
Line Of Credit Facility [Line Items]
Lines of credit		$ 13,200,000	$ 35,659,200
Bankers Trust Non-operating [Member]
Line Of Credit Facility [Line Items]
Debt instrument, maturity date		Mar. 31, 2020
Bankers Trust Operating [Member]
Line Of Credit Facility [Line Items]
Lines of credit		$ 0	0
Unsecured Lines of Credit [Member]
Line Of Credit Facility [Line Items]
Lines of credit		13,200,000	35,659,200
Line of credit facility maximum borrowing capacity		60,000,000	60,000,000
Unsecured Lines of Credit [Member] | 4.93% Interest Bearing Line of Credit [Member] | Bankers Trust Non-operating [Member]
Line Of Credit Facility [Line Items]
Lines of credit		13,200,000
Line of credit facility maximum borrowing capacity		$ 50,000,000
Debt instrument, maturity date		Jun. 30, 2021
Variable / Fixed	[1]	Variable
Reset Frequency		Monthly
Line of credit facility, interest rate during period		4.58%
Unsecured Lines of Credit [Member] | 5.68% Interest Bearing Line of Credit [Member] | Bankers Trust Operating [Member]
Line Of Credit Facility [Line Items]
Line of credit facility maximum borrowing capacity		$ 10,000,000
Debt instrument, maturity date		Jun. 30, 2021
Variable / Fixed	[1]	Variable
Reset Frequency		Monthly
Line of credit facility, interest rate during period		5.33%
Unsecured Lines of Credit [Member] | 5.38% Interest Bearing Line of Credit [Member] | Bankers Trust Non-operating [Member]
Line Of Credit Facility [Line Items]
Lines of credit			35,659,200
Line of credit facility maximum borrowing capacity			$ 50,000,000
Debt instrument, maturity date			Jun. 30, 2020
Variable / Fixed	[1]		Variable
Reset Frequency			Monthly
Line of credit facility, interest rate during period			5.38%
Unsecured Lines of Credit [Member] | 5.63% Interest Bearing Line of Credit [Member] | Bankers Trust Operating [Member]
Line Of Credit Facility [Line Items]
Line of credit facility maximum borrowing capacity			$ 10,000,000
Debt instrument, maturity date			Jun. 30, 2020
Variable / Fixed	[1]		Variable
Reset Frequency			Monthly
Line of credit facility, interest rate during period			5.63%

[1] The variable rate is indexed to LIBOR plus an applicable margin.