Commitments and Contingencies (Narrative) (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) obligation	Dec. 31, 2017 USD ($)
Commitments and Contingencies (Textuals) [Abstract]
Number of outstanding letters of credit | obligation	14
Outstanding letters of credit	$ 50,805,000
Outstanding construction financings for leased properties	194,365,000	$ 237,746,000
Additional financing to complete construction	436,984,000
Agreement to acquire outpatient medical facilities	1,250,000,000
Total contingent purchase obligations	$ 17,309,000
Expense recognized for the donation of the corporate headquarters		$ 40,730,000
Minimum part of economic life of leased asset to be classified as capital lease	75.00%
Minimum net present value of future minimum lease payments to be classified as capital lease	90.00%
Operating lease obligations relating to certain ground leases	$ 1,138,046,000
Aggregate future minimum rentals to be received	$ 72,789,000