Financial Instruments and Fair Value Measurements - Carrying Amounts and Estimated Fair Values of Debt (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	$ 11,934,355	$ 9,380,199
Fair Value of Debt	12,310,220	10,080,157
Credit Facilities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	207,978
Fair Value of Debt	208,029
Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	6,622,440	6,076,920
Fair Value of Debt	6,884,123	6,593,657
Exchangeable Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt		456,766
Fair Value of Debt		511,931
Secured Mortgage Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	785,480	1,050,591
Fair Value of Debt	886,632	1,173,488
Term Loans and Other Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	2,458,496	588,816
Fair Value of Debt	2,460,662	591,810
Secured Mortgage Debt of Consolidated Entities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	1,859,961	1,207,106
Fair Value of Debt	$ 1,870,774	$ 1,209,271