Financial Instruments - Debt Instruments with Carrying Values Different than Estimated Fair Values (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior notes	$ 3,118,656	$ 2,765,893
Revolving Credit Facilities and Term Loans	895,000	779,009
Mortgage indebtedness	1,209,921	1,689,805
Total indebtedness	5,223,577	5,234,707
Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior notes	3,276,118	3,011,374
Revolving Credit Facilities and Term Loans	896,899	786,922
Mortgage indebtedness	1,239,663	1,741,855
Total indebtedness	$ 5,412,680	$ 5,540,151