Unconsolidated Entities - Summary of Outstanding Unconsolidated Co-investment Ventures (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014 Property sqft	Dec. 31, 2013 Property sqft	Mar. 31, 2013 Property sqft
Schedule Of Equity Method Investments Joint Ventures [Line Items]
Total assets	$ 24,655,148	$ 24,572,307
Unconsolidated Co-Investment Ventures [Member]
Schedule Of Equity Method Investments Joint Ventures [Line Items]
Number of properties owned	1,342	1,323	1,371
Square feet	269,126,000	264,293,000	267,632,000
Total assets	24,241,378	23,865,250	22,693,952
Investment Management [Member] | Unconsolidated Co-Investment Ventures [Member] | Americas [Member]
Schedule Of Equity Method Investments Joint Ventures [Line Items]
Number of properties owned	712	709	804
Square feet	109,147,000	108,537,000	127,869,000
Total assets	8,074,306	8,014,339	9,329,047
Investment Management [Member] | Unconsolidated Co-Investment Ventures [Member] | Europe [Member]
Schedule Of Equity Method Investments Joint Ventures [Line Items]
Number of properties owned	585	571	514
Square feet	136,647,000	132,876,000	119,736,000
Total assets	12,119,512	11,818,786	9,698,216
Investment Management [Member] | Unconsolidated Co-Investment Ventures [Member] | Asia [Member]
Schedule Of Equity Method Investments Joint Ventures [Line Items]
Number of properties owned	45	43	53
Square feet	23,332,000	22,880,000	20,027,000
Total assets	$ 4,047,560	$ 4,032,125	$ 3,666,689