Notes Payable - Summary of Notes Payable (Details) $ in Thousands			9 Months Ended
	Oct. 09, 2020 day extension	Oct. 01, 2018 extension	Sep. 30, 2020 USD ($) extension	Dec. 31, 2019 USD ($)
Debt Instrument [Line Items]
Long-term debt, gross			$ 306,637	$ 306,793
Less: unamortized deferred loan costs			(3,009)	(3,754)
Long-term debt			$ 303,628	303,039
Notes Payable to Banks | Hartman SPE, LLC
Debt Instrument [Line Items]
Number of extensions | extension		3	3
Extension term		1 year	1 year
Debt yield, minimum			12.50%
Notes Payable to Banks | Hartman SPE, LLC | Subsequent Event
Debt Instrument [Line Items]
Number of extensions | extension	2
Extension term	1 year
Minimum | Notes Payable to Banks | Hartman SPE, LLC | Subsequent Event
Debt Instrument [Line Items]
Days from current maturity date to exercise extension option | day	30
Maximum | Notes Payable to Banks | Hartman SPE, LLC | Subsequent Event
Debt Instrument [Line Items]
Days from current maturity date to exercise extension option | day	60
Richardson Heights
Debt Instrument [Line Items]
Effective interest rate			4.61%
Long-term debt, gross			$ 16,824	17,260
Cooper Street
Debt Instrument [Line Items]
Effective interest rate			4.61%
Long-term debt, gross			$ 7,264	7,435
Bent Tree Green
Debt Instrument [Line Items]
Effective interest rate			4.61%
Long-term debt, gross			$ 7,264	7,435
Mitchelldale
Debt Instrument [Line Items]
Effective interest rate			4.61%
Long-term debt, gross			$ 11,004	11,263
Hartman SPE, LLC
Debt Instrument [Line Items]
Effective interest rate			1.95%
Long-term debt, gross			$ 259,000	259,000
Extension term			1 year
Debt yield, minimum			12.50%
EWB - SBA PPP
Debt Instrument [Line Items]
Effective interest rate			0.00%
Long-term debt, gross			$ 2,492	0
Hartman XXI - Maturing October 31, 2021
Debt Instrument [Line Items]
Effective interest rate			10.00%
Long-term debt, gross			$ 2,789	$ 4,400