Summary of Significant Accounting Policies - Noncontrolling Interests (Details)						3 Months Ended			9 Months Ended
	Jan. 31, 2017 USD ($) shares	Jan. 12, 2017 USD ($)	Dec. 17, 2015 USD ($) shares	Mar. 01, 2015 USD ($)	Feb. 05, 2015 USD ($) $ / shares shares	Sep. 30, 2017 USD ($) acquisitions	Jun. 30, 2017 acquisitions	Mar. 31, 2017 USD ($) shares	Sep. 30, 2017 USD ($) Rate	Dec. 31, 2016 USD ($)	Apr. 01, 2016 USD ($)
Business Acquisition [Line Items]
Purchase price						$ 190,183,000			$ 1,000,000,000.0
Percentage of interest held | Rate									97.10%
Operating partnership units redemption ratio									1
Fair value of embedded derivative		$ 5,600,000				$ 0			$ 0	$ 5,571,000
Equity method investment received				$ 5,000,000
Internal rate of return				15.00%
Number Of Acquisitions Funded Through Issuance of OP Units | acquisitions						0	0
Noncontrolling interest redeemed for cash						$ 1,100,000			$ 1,100,000
Operating Partnership
Business Acquisition [Line Items]
Purchase price								$ 78,600,000
Units | Operating Partnership
Business Acquisition [Line Items]
Number of units issued for funding purchase price | shares								2,247,817
Supplemental disclosure of noncash activity - issuance of OP Units and Series A Preferred Units in connection with acquisitions								$ 44,300,000
Joint venture, Operating Partnership and Medical Center of New Albany I, LLC
Business Acquisition [Line Items]
Supplemental disclosure of noncash activity - issuance of OP Units and Series A Preferred Units in connection with acquisitions	$ 2,800,000
Payments to acquire businesses, gross	$ 2,100,000
Joint venture, Operating Partnership and Medical Center of New Albany I, LLC | Units | Operating Partnership
Business Acquisition [Line Items]
Decrease from redemptions or purchase of interests (in shares) | shares	38,641
Minnetonka MOB
Business Acquisition [Line Items]
Number of units issued for funding purchase price | shares					44,685
Consideration transferred, equity interests issued and issuable					$ 9,700,000
Minnetonka MOB | Units
Business Acquisition [Line Items]
Preferred shares value redeemed											$ 9,800,000
Fair value of embedded derivative											$ 2,700,000
Nashville MOB
Business Acquisition [Line Items]
Number of units issued for funding purchase price | shares			91,236
Payments to acquire businesses, gross		$ 20,000,000.0
Consideration transferred, equity interests issued and issuable			$ 19,700,000
Series A Preferred Units
Business Acquisition [Line Items]
Cumulative preferred return					5.00%
Redeemable noncontrolling interest, equity, preferred, redemption shares in exchange					1
Redemption value (in dollars per share) | $ / shares					$ 200
Period in which preferred units will be redeemable					1 year