Notes Payable - Additional Information (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Unsecured Debt [Member]	Jun. 14, 2013 Unsecured Debt [Member] $250 million unsecured term loan [Member]	Mar. 01, 2012 Unsecured Debt [Member] $150 million unsecured term loan [Domain]	Oct. 16, 2013 Unsecured Debt [Member] Senior Guaranteed Notes	Sep. 30, 2013 Unsecured Debt [Member] Senior Guaranteed Notes	Aug. 07, 2013 Unsecured Debt [Member] $500 million unsecured revolving credit faciltiy [Member] [Member]	Sep. 30, 2013 Unsecured Debt [Member] Variable Rate Debt	Sep. 30, 2013 Secured Debt [Member]		Sep. 30, 2013 Secured Debt [Member] Fixed Rate Debt	Sep. 30, 2013 Secured Debt [Member] Variable Rate Debt		Sep. 30, 2013 Unsecured Debt [Member]	Sep. 30, 2013 Minimum [Member] $150 million unsecured term loan [Domain]	Mar. 01, 2012 Minimum [Member] $150 million unsecured term loan [Domain]	Aug. 07, 2013 Minimum [Member] Unsecured Debt [Member] $500 million unsecured revolving credit faciltiy [Member] [Member]	Sep. 30, 2013 Maximum [Member] $150 million unsecured term loan [Domain]	Mar. 01, 2012 Maximum [Member] $150 million unsecured term loan [Domain]	Aug. 07, 2013 Maximum [Member] Unsecured Debt [Member] $500 million unsecured revolving credit faciltiy [Member] [Member]	Sep. 30, 2013 Tranche 1 [Member] Unsecured Debt [Member] Senior Guaranteed Notes	Sep. 30, 2013 Tranche 2 [Member] Unsecured Debt [Member] Senior Guaranteed Notes	Sep. 30, 2013 Tranche 3 [Member] Unsecured Debt [Member] Senior Guaranteed Notes	Sep. 30, 2013 Tranche 4 [Member] Unsecured Debt [Member] Senior Guaranteed Notes	Sep. 30, 2013 Designated as Hedging Instrument [Member] Interest Rate Swap [Member] Contract	Sep. 30, 2013 Designated as Hedging Instrument [Member] Interest Rate Caps Contract	Sep. 30, 2013 Not Designated as Hedging Instrument [Member] Interest Rate Caps Contract
Debt Instrument [Line Items]
Notes Payable	$ 1,860,000,000	$ 1,670,000,000							$ 350,000,000	$ 1,050,202,000	[1]	$ 691,817,000	$ 358,385,000	[1]	$ 810,000,000
Debt Instrument, Face Amount				250,000,000	150,000,000	350,000,000	175,000,000	500,000,000														18,000,000	20,000,000	117,000,000	20,000,000
Debt Instrument, Interest Rate, Stated Percentage						4.30%																3.15%	3.61%	4.17%	4.33%
Debt Instrument, Basis Spread on Variable Rate				1.30%												1.10%	1.40%	0.90%	2.05%	2.15%	1.70%
Secured credit facility as a Percentage of outstanding debt	35.00%
Notional																										$ 559,000,000	$ 224,600,000	$ 63,800,000
Derivative, Number of Instruments Held																										18	12	11
Debt Instrument, Interest Rate, Effective Percentage	3.20%		2.70%						1.30%

[1] Includes capped balances.