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Debt - Debt Summary (Parenthetical) (Detail)
$ in Thousands
12 Months Ended
Dec. 31, 2017
USD ($)
Property
Jun. 30, 2017
Dec. 31, 2016
USD ($)
Debt Instrument [Line Items]      
Debt $ 9,412,631   $ 10,608,294
Effective Interest Rate   2.30%  
Cost of properties securing mortgage debt $ 2,200,000    
Count of properties securing mortgage debt | Property 144    
Cost of properties securing mortgage debt of consolidated entities $ 300,000    
Number of properties securing mortgage debt of consolidated entities | Property 18    
Senior Notes [Member]      
Debt Instrument [Line Items]      
Debt $ 6,067,277   6,417,492
Secured Mortgages [Member]      
Debt Instrument [Line Items]      
Debt $ 808,096   $ 979,585
Minimum [Member] | Secured Mortgage Debt of Consolidated Entities [Member]      
Debt Instrument [Line Items]      
Effective Interest Rate 2.90%    
Debt Instrument maturity date 2019-04    
Minimum [Member] | Senior Notes [Member]      
Debt Instrument [Line Items]      
Effective Interest Rate 1.50%    
Debt Instrument maturity date 2020-10    
Minimum [Member] | Secured Mortgages [Member]      
Debt Instrument [Line Items]      
Effective Interest Rate 2.70%    
Debt Instrument maturity date 2018-05    
Maximum [Member] | Secured Mortgage Debt of Consolidated Entities [Member]      
Debt Instrument [Line Items]      
Effective Interest Rate 3.40%    
Debt Instrument maturity date 2027-12    
Maximum [Member] | Senior Notes [Member]      
Debt Instrument [Line Items]      
Effective Interest Rate 4.40%    
Debt Instrument maturity date 2029-06    
Maximum [Member] | Secured Mortgages [Member]      
Debt Instrument [Line Items]      
Effective Interest Rate 7.80%    
Debt Instrument maturity date 2025-12    
EUR      
Debt Instrument [Line Items]      
Debt $ 3,800,000    
JPY      
Debt Instrument [Line Items]      
Debt 1,300,000    
CAD      
Debt Instrument [Line Items]      
Debt 500,000    
GBP      
Debt Instrument [Line Items]      
Debt $ 700,000