Recently Issued Accounting Literature (Narrative) (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Jan. 01, 2019 USD ($) ground_lease	Dec. 31, 2018 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of properties subject to ground leases | ground_lease					12
Right-of-use assets	$ 370,604		$ 370,604			$ 0
Lease liabilities	490,978		490,978			$ 0
Capitalized lease costs		$ 1,444		$ 3,883
Decrease in lease revenues	(414,343)		(1,310,881)
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use assets					$ 526,866
Lease liabilities					$ 526,866
Decrease in lease revenues	$ 1,106		$ 16,488