Real Estate - Investments in Real Estate Properties (Detail) ft² in Thousands, $ in Thousands	Dec. 31, 2017 USD ($) ft² a Buildings	Dec. 31, 2016 USD ($) ft² a Buildings
Real Estate Properties [Line Items]
Total investments in real estate properties	$ 25,838,644	$ 27,119,330
Less accumulated depreciation	4,059,348	3,758,372
Net investments in real estate properties	$ 21,779,296	$ 23,360,958
Improved Land [Member]
Real Estate Properties [Line Items]
Square Feet | ft²	0	0
Number of buildings | Buildings	0	0
Total investments in real estate properties	$ 5,735,978	$ 6,037,543
Building and Improvements [Member]
Real Estate Properties [Line Items]
Square Feet | ft²	294,811	331,210
Number of buildings | Buildings	1,525	1,776
Total investments in real estate properties	$ 16,849,349	$ 17,905,914
Development Portfolio, Including Cost of Land: Pre-stabilized [Member]
Real Estate Properties [Line Items]
Square Feet | ft²	7,345	8,256
Number of buildings | Buildings	22	29
Total investments in real estate properties	$ 546,173	$ 798,233
Properties Under Development [Member]
Real Estate Properties [Line Items]
Square Feet | ft²	22,216	19,539
Number of buildings | Buildings	63	60
Total investments in real estate properties	$ 1,047,316	$ 633,849
Land [Member]
Real Estate Properties [Line Items]
Square Feet | a	5,191	5,892
Total investments in real estate properties	$ 1,154,383	$ 1,218,904
Other Real Estate Investments [Member]
Real Estate Properties [Line Items]
Square Feet | ft²	0	0
Number of buildings | Buildings	0	0
Total investments in real estate properties	$ 505,445	$ 524,887