Rent Expense - Additional Information (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) properties healthcareproperty	Mar. 31, 2017 USD ($)
Operating Leased Assets [Line Items]
Number of properties subject to parking lease	2
Number of properties subject to air space lease | healthcareproperty	1
Number of properties subject to ground leases	77
Number of office space leases	4
Maximum lease terms	87 years
Operating Expense | Parking, Air And Ground Leases
Operating Leased Assets [Line Items]
Rent expenses for parking, air, and ground leases | $	$ 0.6	$ 0.6