Notes Payable - Additional Information (Detail) (USD $)	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2012 Fixed Rate Debt	Dec. 31, 2011 Fixed Rate Debt	Mar. 01, 2012 Unsecured Debt [Member] $150 million unsecured term loan [Domain]	Mar. 31, 2012 Interest Rate Swaps	Mar. 31, 2012 Interest Rate Caps	Mar. 31, 2012 Not Designated as Hedging Instrument [Member]	Mar. 31, 2012 Unsecured Debt [Member]	Mar. 31, 2012 Unsecured Debt [Member] L I B O R [Member] Fixed Rate Debt		Mar. 31, 2012 Unsecured Debt [Member] Senior Guaranteed Notes Fixed Rate Debt	Mar. 01, 2012 Minimum $150 million unsecured term loan [Domain]	Mar. 01, 2012 Maximum $150 million unsecured term loan [Domain]
Debt Instrument [Line Items]
Notes Payable	$ 1,540,056,000	$ 1,649,755,000	$ 537,000,000	$ 538,000,000					$ 187,000,000	$ 50,000,000	[1]	$ 135,000,000
Debt Instrument, Face Amount					150,000,000
Debt Instrument, Basis Spread on Variable Rate													1.40%	2.15%
Secured credit facility as a Percentage of outstanding debt	64.00%
Number of interest rate contracts						24	18
Notional						$ 651,800,000	$ 256,371,000	$ 14,280,000
Derivative, Number of Instruments Held								3

[1] Balance is fixed at 2.7% by interest rate swaps that do not become effective until June 1, 2012. The unswapped rate has been used in this table.