Real Estate - Summary of Dispositions (Detail) ft² in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) ft² Property	Dec. 31, 2016 USD ($) ft² Property	Dec. 31, 2015 USD ($) ft² Property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square feet | ft²	6,859	1,823	7,375
Gains on dispositions of investments in real estate and revaluation of equity investments upon acquisition of a controlling interest, net	$ 1,182,965	$ 757,398	$ 758,887
Continuing Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total gains on contributions and dispositions, net	1,121,745	621,109	758,887
Gains on dispositions of investments in real estate and revaluation of equity investments upon acquisition of a controlling interest, net	$ 1,182,965	$ 757,398	$ 758,887
Continuing Operations [Member] | Contributions to unconsolidated co-investment ventures [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of buildings | Property	222	35	31
Square feet | ft²	48,171	11,624	8,355
Net proceeds	$ 3,201,986	$ 1,231,878	$ 835,385
Gains on contributions, dispositions, revaluations or redemptions, net	$ 847,034	$ 267,441	$ 148,987
Continuing Operations [Member] | Dispositions to Third Parties [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of buildings | Property	110	172	136
Square feet | ft²	17,147	20,360	23,024
Net proceeds	$ 1,281,501	$ 1,760,048	$ 2,352,645
Gains on contributions, dispositions, revaluations or redemptions, net	274,711	353,668	609,900
Continuing Operations [Member] | Revaluation of equity investments upon acquisition of controlling interest and redemption of investment in co-investment ventures [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gains on contributions, dispositions, revaluations or redemptions, net	61,220	0	0
Continuing Operations [Member] | Redemptions of investments in co-investment ventures [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gains on contributions, dispositions, revaluations or redemptions, net	$ 0	$ 136,289	$ 0