Organization and Basis of Presentation - Ground Leases (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) properties	Mar. 31, 2018 USD ($)
Lessee, Lease, Description [Line Items]
Leasing expense	$ 3,208	$ 2,812
Number of properties subject to ground lease (in properties) | properties	5
Weighted average remaining lease term	47 years
Term of contract	11 years
Useful life increase interval	5 years
Weighted average discount rate	4.60%
Leasing expense	$ 468
Cash portion of lease expense	$ 433
Minimum
Lessee, Lease, Description [Line Items]
Renewal term	25 years
Weighted average discount rate	4.10%
Maximum
Lessee, Lease, Description [Line Items]
Term of contract	110 years
Renewal term	48 years
Weighted average discount rate	5.00%
Accounting Standards Update 2016-02
Lessee, Lease, Description [Line Items]
Leasing expense	$ 300