Borrowings Under Credit Facilities and Related Items (Details Textual)	9 Months Ended
	Sep. 30, 2018 USD ($) properties
Line of Credit Facility [Line Items]
Number of banks in consortium | properties	31
Available to borrow in alternate currencies	$ 1,000,000,000
Debt instrument, basis spread on variable rate	0.825%
Line of credit facility, commitment fee percentage	0.15%
Revolving Credit Facility
Line of Credit Facility [Line Items]
Unsecured line of credit arrangement	$ 3,000,000,000
Term Credit Facility
Line of Credit Facility [Line Items]
Unsecured line of credit arrangement	500,000,000
Term Credit Facility, CAD Denominated
Line of Credit Facility [Line Items]
Unsecured line of credit arrangement	$ 250,000,000
London Interbank Offered Rate (LIBOR) | Revolving Credit Facility
Line of Credit Facility [Line Items]
Debt instrument, interest rate during period	3.09%
Accordion Feature [Member]
Line of Credit Facility [Line Items]
Unsecured line of credit arrangement	$ 1,000,000,000
Accordion Feature [Member] | Term Credit Facility, CAD Denominated
Line of Credit Facility [Line Items]
Unsecured line of credit arrangement	$ 250,000,000