Summary of Significant Accounting Policies (Narrative) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Jan. 01, 2019 USD ($) property
Finite-Lived Intangible Assets [Line Items]
Weighted average remaining lease term	6 years 1 month 12 days
Number of properties subject to ground leases | property			1
Operating lease right-of-use asset	$ 55,730		$ 54,900
Operating lease liability	54,898		54,900
Tenant reimbursements	17,051	$ 15,229
Accounting Standards Update 2016-02
Finite-Lived Intangible Assets [Line Items]
Straight-line rent liability			2,700
Prepaid rent			1,200
Accounting Standards Update 2016-02 | Below-market ground lease
Finite-Lived Intangible Assets [Line Items]
Below market ground lease intangible asset			$ 2,400
Tenant Reimbursement And Other Revenue
Finite-Lived Intangible Assets [Line Items]
Tenant reimbursements	$ 100