Financial Instruments and Fair Value Measurements - Carrying Amounts and Estimated Fair Values of Debt (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	$ 8,822,952	$ 9,011,216
Fair Value of Debt	9,431,906	9,586,791
Credit Facilities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	741,610	725,483
Fair Value of Debt	741,610	725,679
Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	5,443,138	5,357,933
Fair Value of Debt	5,885,585	5,698,864
Exchangeable Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	451,999	438,481
Fair Value of Debt	485,077	514,381
Secured Mortgage Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	1,141,772	1,696,597
Fair Value of Debt	1,272,061	1,840,829
Secured Mortgage Debt of Consolidated Entities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	26,064	239,992
Fair Value of Debt	26,678	246,324
Term Loan and Other Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	1,018,369	552,730
Fair Value of Debt	$ 1,020,895	$ 560,714