Financial Instruments - Debt Instruments with Carrying Values Different than Estimated Fair Values (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior notes	$ 2,765,893	$ 2,754,120
Revolving Credit Facilities and Term Loans	779,009	779,133
Mortgage indebtedness	1,689,805	1,761,421
Total indebtedness	5,234,707	5,294,674
Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior notes	3,011,374	2,991,698
Revolving Credit Facilities and Term Loans	786,922	787,772
Mortgage indebtedness	1,741,855	1,779,375
Total indebtedness	$ 5,540,151	$ 5,558,845