Nature of Business and Financial Statement Presentation - Non-cash Investing and Financing Activities (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Other Significant Noncash Transactions [Line Items]
Mortgages assumed from acquisitions			$ 33,700	$ 293,300
Issuance of Operating Partnership Units ("OP Units")			0	18,300
Redemption of OP Units			18,300	0
Preferred equity interest and mezzanine loan applied to purchase price of acquired properties			0	51,800
Elimination of a previously held equity interest			1,400	2,800
Accounts payable related to construction in progress			43,900	31,300
Dividends declared	$ 68,059	$ 61,300	68,059	61,300	$ 61,468
Write-off of preferred share original issuance costs	$ 0	$ 0	0	1,943
Accumulated Other Comprehensive Loss
Other Significant Noncash Transactions [Line Items]
Reclassification adjustment of foreign currency translation			$ 0	$ 21,400