Related Party Transactions - Narrative (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018 USD ($) investment	Mar. 31, 2017 USD ($)	Mar. 31, 2018 USD ($) investment	Mar. 31, 2017 USD ($)
Related Party Transaction [Line Items]
Related party expense	$ 317	$ 302	$ 619	$ 589
Related party - general and administrative	146	103	228	182
Real Property Management Real Estate Brokerage And Construction Supervision Services | Majestic Property Management Corporation
Related Party Transaction [Line Items]
Related party expense	10	8	19	16
Shared Services Agreement | Gould Investors Limited Partnership
Related Party Transaction [Line Items]
Related party - general and administrative	147	103	228	182
Affiliated Entity
Related Party Transaction [Line Items]
Related party expense	$ 908	672	$ 1,767	1,296
Number of investments | investment	2		2
Affiliated Entity | Payment Of Acquisition Fee
Related Party Transaction [Line Items]
Related party expense	$ 1,300	$ 350	$ 1,530	$ 650