Selected Quarterly Financial Data (unaudited) (Details) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017 USD ($) real_estate_property $ / shares	Sep. 30, 2017 USD ($) real_estate_property $ / shares	Jun. 30, 2017 USD ($) real_estate_property $ / shares	Mar. 31, 2017 USD ($) real_estate_property $ / shares	Dec. 31, 2016 USD ($) real_estate_property $ / shares	Sep. 30, 2016 USD ($) real_estate_property $ / shares	Jun. 30, 2016 USD ($) real_estate_property $ / shares	Mar. 31, 2016 USD ($) real_estate_property $ / shares	Dec. 31, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($) real_estate_property $ / shares	Dec. 31, 2015 USD ($) $ / shares
Subsidiary, Sale of Stock [Line Items]
Revenues	$ 10,962	$ 9,444	$ 8,930	$ 8,007	$ 7,392	$ 6,443	$ 6,196	$ 5,166	$ 37,343	$ 25,197	$ 8,632
Expenses	8,363	7,838	7,256	6,499	5,970	5,203	5,485	4,670	29,956	21,328	9,759
Other income (expense)	(1,047)	(1,027)	(1,208)	(595)	(389)	(176)	(203)	(380)	(3,877)	(1,148)	(329)
Net loss	$ 1,552	$ 579	$ 466	$ 913	$ 1,033	$ 1,064	$ 508	$ 116	$ 2,779	$ 2,721	$ (1,456)
Net income (loss) per basic common share (in dollars per share) | $ / shares	$ 0.08	$ 0.02	$ 0.04	$ 0.07	$ 0.08	$ 0.08	$ 0.04	$ 0.02	$ 0.19	$ 0.24	$ (0.31)
Net income (loss) per diluted common share (in dollars per share) | $ / shares	$ 0.08	$ 0.02	$ 0.04	$ 0.07	$ 0.08	$ 0.08	$ 0.04	$ 0.02	$ 0.19	$ 0.24	$ (0.31)
Number of real estate properties acquired | real_estate_property	6	2	10	10	6	4	3	4		14
Acquisitions During 2016 [Member]
Subsidiary, Sale of Stock [Line Items]
Expenses										$ 800