Notes Payable, net - Summary of Notes Payable (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2020 USD ($) extension	Dec. 31, 2019 USD ($)
Debt Instrument [Line Items]
Long-term debt, gross	$ 309,871	$ 306,793
Less: unamortized deferred loan costs	(3,247)	(3,754)
Long-term debt	$ 306,624	303,039
Richardson Heights
Debt Instrument [Line Items]
Effective interest rate	4.61%
Long-term debt, gross	$ 16,956	17,260
Cooper Street
Debt Instrument [Line Items]
Effective interest rate	4.61%
Long-term debt, gross	$ 7,316	7,435
Bent Tree Green
Debt Instrument [Line Items]
Effective interest rate	4.61%
Long-term debt, gross	$ 7,316	7,435
Mitchelldale
Debt Instrument [Line Items]
Effective interest rate	4.61%
Long-term debt, gross	$ 11,083	11,263
Hartman SPE, LLC
Debt Instrument [Line Items]
Effective interest rate	1.96%
Long-term debt, gross	$ 259,000	259,000
Number of extensions | extension	3
Extension term	1 year
Debt instrument, covenant, debt yield, minimum	12.50%
Hartman XXI
Debt Instrument [Line Items]
Effective interest rate	10.00%
Long-term debt, gross	$ 8,200	$ 4,400