Financial Instruments and Fair Value Measurements - Carrying Amounts and Estimated Fair Values of Debt (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	$ 8,529,453	$ 9,011,216
Fair Value of Debt	9,230,044	9,586,791
Credit Facilities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	38,673	725,483
Fair Value of Debt	38,673	725,679
Senior notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	6,119,885	5,357,933
Fair Value of Debt	6,597,905	5,698,864
Exchangeable senior notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	447,321	438,481
Fair Value of Debt	514,694	514,381
Secured Mortgage Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	1,271,546	1,696,597
Fair Value of Debt	1,424,379	1,840,829
Secured mortgage debt of consolidated entities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	26,804	239,992
Fair Value of Debt	27,484	246,324
Term loan and other debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value of Debt	625,224	552,730
Fair Value of Debt	$ 626,909	$ 560,714