Real Estate Investments - Acquisitions (Details) $ in Thousands											9 Months Ended
	Oct. 31, 2019 USD ($) ft²	Sep. 30, 2019 USD ($) ft² property	Sep. 26, 2019 USD ($)	Aug. 01, 2019 USD ($) ft²	Jun. 26, 2019 USD ($) ft²	Jun. 14, 2019 USD ($) ft²	Jun. 11, 2019 USD ($) ft²	Jun. 10, 2019 USD ($) ft²	Apr. 02, 2019 USD ($) ft²	Mar. 28, 2019 USD ($) ft² property Lease	Sep. 30, 2019 USD ($) ft² property	Dec. 31, 2018 property
Business Acquisition [Line Items]
Number of properties subject to ground leases | property		108									108	107
Financing lease liabilities		$ 14,305									$ 14,305
Real Estate Acquisition
Business Acquisition [Line Items]
Purchase price											273,900
Cash consideration											271,200
Real Estate		276,200									276,200
Other		$ (5,000)									$ (5,000)
Square footage | ft²		769,282									769,282
Medical Office Building | Washington, D.C. (4) | Real Estate Acquisition
Business Acquisition [Line Items]
Date Acquired										Mar. 28, 2019
Purchase price										$ 46,000
Cash consideration										45,900
Real Estate										50,200
Other										$ (4,300)
Square footage | ft²										158,338
Number of properties acquired | property										2
Number of properties subject to ground leases | Lease										2
Financing lease liabilities		$ 14,300									$ 14,300
Above-market lease intangibles		$ 5,200									$ 5,200
Medical Office Building | Indianapolis, IN (5) | Real Estate Acquisition
Business Acquisition [Line Items]
Date Acquired										Mar. 28, 2019
Purchase price										$ 47,000
Cash consideration										44,800
Real Estate										43,700
Other										$ 1,100
Square footage | ft²										143,499
Prepaid ground leases										$ 800
Below-market lease intangible										$ 900
Medical Office Building | Atlanta, GA | Real Estate Acquisition
Business Acquisition [Line Items]
Date Acquired									Apr. 02, 2019
Purchase price									$ 28,000
Cash consideration									28,000
Real Estate									28,000
Other									$ 0
Square footage | ft²									47,963
Medical Office Building | Dallas, TX | Real Estate Acquisition
Business Acquisition [Line Items]
Date Acquired								Jun. 10, 2019
Purchase price								$ 17,000
Cash consideration								16,700
Real Estate								17,000
Other								$ (300)
Square footage | ft²								89,990
Medical Office Building | Seattle, WA | Real Estate Acquisition
Business Acquisition [Line Items]
Date Acquired					Jun. 28, 2019	Jun. 14, 2019	Jun. 11, 2019
Purchase price					$ 30,500	$ 19,000	$ 7,700
Cash consideration					30,400	19,100	7,800
Real Estate					30,600	19,500	7,800
Other					$ (200)	$ (400)	$ 0
Square footage | ft²					78,288	47,255	29,870
Medical Office Building | Houston, TX | Real Estate Acquisition
Business Acquisition [Line Items]
Date Acquired				Aug. 01, 2019
Purchase price				$ 13,500
Cash consideration				13,500
Real Estate				13,500
Other				$ 0
Square footage | ft²				29,903
Medical Office Building | Oklahoma City, OK | Real Estate Acquisition
Business Acquisition [Line Items]
Date Acquired			Sep. 26, 2019
Purchase price			$ 4,100
Cash consideration			4,100
Real Estate			4,100
Other			$ 0
Square footage | ft²		28,542									28,542
Medical Office Building | Los Angeles, CA (6) | Real Estate Acquisition
Business Acquisition [Line Items]
Date Acquired		Sep. 30, 2019
Purchase price		$ 61,100
Cash consideration		60,900
Real Estate		61,800									$ 61,800
Other		$ (900)									$ (900)
Square footage | ft²		115,634									115,634
Number of properties acquired | property		2
Subsequent Event | Medical Office Building | Dallas, TX | Real Estate Acquisition
Business Acquisition [Line Items]
Purchase price	$ 20,100
Square footage | ft²	48,192
Subsequent Event | Medical Office Building | Raleigh, North Carolina | Real Estate Acquisition
Business Acquisition [Line Items]
Purchase price	$ 21,600
Square footage | ft²	57,730