Unconsolidated Entities - Summary of Unconsolidated Co-investment Ventures (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Jun. 30, 2014 sqft	Dec. 31, 2013	Sep. 30, 2014 Unconsolidated Co-Investment Ventures [Member] Property sqft	Dec. 31, 2013 Unconsolidated Co-Investment Ventures [Member] sqft Property	Sep. 30, 2013 Unconsolidated Co-Investment Ventures [Member] Property sqft	Sep. 30, 2014 Investment Management [Member] Unconsolidated Co-Investment Ventures [Member] Americas [Member] Property sqft	Dec. 31, 2013 Investment Management [Member] Unconsolidated Co-Investment Ventures [Member] Americas [Member] sqft Property	Sep. 30, 2013 Investment Management [Member] Unconsolidated Co-Investment Ventures [Member] Americas [Member] sqft Property	Sep. 30, 2014 Investment Management [Member] Unconsolidated Co-Investment Ventures [Member] Europe [Member] Property sqft	Dec. 31, 2013 Investment Management [Member] Unconsolidated Co-Investment Ventures [Member] Europe [Member] Property sqft	Sep. 30, 2013 Investment Management [Member] Unconsolidated Co-Investment Ventures [Member] Europe [Member] sqft Property	Sep. 30, 2014 Investment Management [Member] Unconsolidated Co-Investment Ventures [Member] Asia [Member] sqft Property	Dec. 31, 2013 Investment Management [Member] Unconsolidated Co-Investment Ventures [Member] Asia [Member] sqft Property	Sep. 30, 2013 Investment Management [Member] Unconsolidated Co-Investment Ventures [Member] Asia [Member] sqft Property
Schedule Of Equity Method Investments Joint Ventures [Line Items]
Number of properties owned				1,494	1,323	1,308	814	709	737	629	571	534	51	43	37
Square feet		12,600,000		301,751,000	264,293,000	257,569,000	130,476,000	108,537,000	114,042,000	145,332,000	132,876,000	124,794,000	25,943,000	22,880,000	18,733,000
Total assets	$ 24,072,103		$ 24,572,307	$ 25,713,935	$ 23,865,250	$ 23,382,115	$ 9,395,900	$ 8,014,339	$ 8,433,418	$ 11,951,749	$ 11,818,786	$ 11,471,358	$ 4,366,286	$ 4,032,125	$ 3,477,339