Fair Value Disclosure of Financial Instruments - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Renovations to Existing Real Estate Assets	$ 8,616,000	$ 11,070,000
Notes Payable	1,860,000,000		1,670,000,000
Fixed Rate Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable, fair value	785,000,000		778,000,000
Notes Payable Excluding Interest Rate Swaps and Cap Agreements	743,000,000		732,000,000
Variable Rate Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable, fair value	1,000,000,000		860,000,000
Notes Payable Excluding Interest Rate Swaps and Cap Agreements	$ 1,100,000,000		$ 941,000,000
Minimum [Member] | Secured Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Renewal Period	30 days
Maximum [Member] | Secured Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Renewal Period	90 days