Unsecured Lines of Credit - Summary of Unsecured Lines of Credit (Details) - USD ($)		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Line Of Credit Facility [Line Items]
Lines of credit		$ 7,475,000	$ 13,200,000
Unsecured Lines of Credit [Member]
Line Of Credit Facility [Line Items]
Lines of credit		7,475,000	13,200,000
Line of credit facility maximum borrowing capacity		60,000,000	60,000,000
Unsecured Lines of Credit [Member] | Bankers Trust Operating [Member]
Line Of Credit Facility [Line Items]
Lines of credit		0
Unsecured Lines of Credit [Member] | 2.65% Interest Bearing Line of Credit [Member] | Bankers Trust Non-operating [Member]
Line Of Credit Facility [Line Items]
Lines of credit		7,475,000
Line of credit facility maximum borrowing capacity		$ 50,000,000
Commitment Maturity		2022-06
Variable / Fixed	[1]	Variable
Reset Frequency		Monthly
Line of credit facility, interest rate during period		2.65%
Unsecured Lines of Credit [Member] | 3.40% 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
Commitment Maturity		2022-06
Variable / Fixed	[1]	Variable
Reset Frequency		Monthly
Line of credit facility, interest rate during period		3.40%
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
Commitment Maturity			2021-06
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
Commitment Maturity			2021-06
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.