Rent Expense - (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) properties healthcareproperty	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Operating Leased Assets [Line Items]
Number of properties pursuant to parking lease	3
Number of properties subject to air space lease | healthcareproperty	1
Number of properties pursuant to ground leases	76
Number of office space leases	5
Maximum lease terms	87 years
Parking, Air And Ground Leases | Operating Expense
Operating Leased Assets [Line Items]
Rent expenses for parking and ground leases | $	$ 2.4	$ 2.4	$ 1.9
Office Leases | Operating Expense
Operating Leased Assets [Line Items]
Rent expenses for parking and ground leases | $	$ 0.1	$ 0.1