Unsecured Lines of Credit - Summary of Unsecured Lines of Credit (Details) - USD ($)		3 Months Ended	12 Months Ended
		Mar. 31, 2020	Dec. 31, 2019
Line Of Credit Facility [Line Items]
Lines of credit		$ 12,540,000	$ 13,200,000
Bankers Trust Non-operating [Member]
Line Of Credit Facility [Line Items]
Debt instrument, maturity date		Jun. 30, 2020
Bankers Trust Operating [Member]
Line Of Credit Facility [Line Items]
Lines of credit		$ 0
Unsecured Lines of Credit [Member]
Line Of Credit Facility [Line Items]
Lines of credit		12,540,000	13,200,000
Line of credit facility maximum borrowing capacity		60,000,000	60,000,000
Unsecured Lines of Credit [Member] | 3.86% Interest Bearing Line of Credit [Member] | Bankers Trust Non-operating [Member]
Line Of Credit Facility [Line Items]
Lines of credit		12,540,000
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		3.86%
Unsecured Lines of Credit [Member] | 4.61% 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		4.61%
Unsecured Lines of Credit [Member] | 4.19% 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			4.19%
Unsecured Lines of Credit [Member] | 4.94% 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			4.94%

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