Summary of Significant Accounting Policies - Non-cash Investing and Financing Activities (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Noncash Or Part Noncash Acquisitions [Line Items]
Mortgages assumed from acquisitions	$ 293,300,000	$ 969,700,000	$ 271,600,000
Issuance of Operating Partnership Units ("OP Units") in connection with acquisitions	18,300,000	0	0
Preferred equity interest and mezzanine loan applied to purchase price of acquired properties	51,775,000	160,123,000	0
Elimination of the previously held equity interest in unconsolidated joint ventures acquired	2,500,000	26,400,000	36,800,000
Reclassification adjustment of foreign currency translation	21,755,000
Accounts payable related to construction in progress	25,700,000	21,500,000	18,200,000
Dividends declared	61,468,000	55,107,000	44,200,000
Write-off of preferred share original issuance costs	1,943,000	5,246,000	5,804,000
Accumulated Other Comprehensive Loss
Noncash Or Part Noncash Acquisitions [Line Items]
Reclassification adjustment of foreign currency translation	$ 21,800,000	$ 0	$ 0