Acquisitions and Dispositions - Additional Information (Detail)	1 Months Ended				3 Months Ended	9 Months Ended
	Jun. 30, 2018 USD ($) Time	Sep. 30, 2017 USD ($) Time	Jul. 31, 2017 USD ($) Time	Mar. 31, 2017 USD ($)	Mar. 31, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($) Time	Sep. 30, 2017 USD ($) Time	Mar. 12, 2017
Business Acquisitions And Dispositions [Line Items]
Cash received from dispositions						$ 0		$ 65,220,000
Repayment of loan					$ 21,400,000
St. Mary's Professional Office Building
Business Acquisitions And Dispositions [Line Items]
Net cash proceeds received from divestiture				$ 57,300,000	$ 57,300,000
Net sale proceeds due							$ 11,300,000
Gain on divestiture of property								$ 27,200,000
Arlington Medical Properties
Business Acquisitions And Dispositions [Line Items]
Total purchase price				$ 7,900,000
Ownership prior to minority interest purchase				85.00%	85.00%
Remaining percentage owned by third party member									15.00%
Beaumont Medical Sleep Center Building
Business Acquisitions And Dispositions [Line Items]
Total purchase price	$ 4,000,000
Percentage of building area leased	100.00%
Initial lease terms	9 years 6 months
Number of term renewal options | Time	2
Additional renewal terms	5 years
Las Palmas Del Sol Emergency Center In El Paso
Business Acquisitions And Dispositions [Line Items]
Total purchase price		$ 4,200,000
Percentage of building area leased		100.00%
Number of term renewal options | Time		2					2	2
Additional renewal terms		5 years
Triple net lease agreement period		10 years
Renewal Term (years)		9 years
The Health Center at Hamburg
Business Acquisitions And Dispositions [Line Items]
Total purchase price			$ 4,700,000
Percentage of building area leased			100.00%
Number of term renewal options | Time			2
Additional renewal terms			5 years
Triple net lease agreement period			15 years
Renewal Term (years)			8 years 6 months