Financial Instruments - Debt Instruments with Carrying Values Different than Estimated Fair Values (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Fair Value Disclosures [Abstract]
Senior notes, Carrying Amount	$ 2,762,893	$ 2,754,120
Revolving Credit Facilities and term loans, Carrying Amount	773,457	779,133
Mortgage indebtedness, Carrying Amount	1,699,694	1,761,421
Total indebtedness	5,236,044	5,294,674
Senior notes, Fair Value	3,000,255	2,991,698
Revolving Credit Facilities and term loans, Fair Value	781,530	787,772
Mortgage indebtedness, Fair Value	1,730,030	1,779,375
Long-term debt, Fair Value Total	$ 5,511,815	$ 5,558,845