Debt Structure (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended		9 Months Ended							9 Months Ended						9 Months Ended							9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Unsecured Debt [Member]	Sep. 30, 2013 Secured Debt [Member]		Sep. 30, 2013 Secured Debt [Member]		Sep. 30, 2013 Unsecured Debt [Member]	Jun. 14, 2013 $250 million unsecured term loan [Member] Unsecured Debt [Member]	Sep. 30, 2013 Fixed Rate Debt Secured Debt [Member]	Sep. 30, 2013 Fixed Rate Debt Term Fixed Loan With Swaps [Member] Unsecured Debt [Member]	Sep. 30, 2013 Fixed Rate Debt Senior Notes [Member] Unsecured Debt [Member]	Sep. 30, 2013 Fixed Rate Debt L I B O R [Member] Secured Debt [Member]	Sep. 30, 2013 Fixed Rate Debt Individual Property Mortgages [Member] Secured Debt [Member]	Sep. 30, 2013 Fixed Rate Debt Secured Debt [Member]	Sep. 30, 2013 Variable Rate Debt Unsecured Debt [Member]	Sep. 30, 2013 Variable Rate Debt Secured Debt [Member]		Sep. 30, 2013 Variable Rate Debt Mortgages [Member] Secured Debt [Member]		Sep. 30, 2013 Variable Rate Debt Secured Debt [Member]		Sep. 30, 2013 FNMA Fixed Rate Debt Conventional Credit Facility [Member] Secured Debt [Member]	Sep. 30, 2013 FNMA Variable Rate Debt Conventional Credit Facility [Member] Secured Debt [Member]		Sep. 30, 2013 FNMA Variable Rate Debt Tax Free Credit Facility [Member] Secured Debt [Member]		Sep. 30, 2013 Freddie Mac Variable Rate Debt Conventional Credit Facility [Member] Secured Debt [Member]		Sep. 30, 2013 Freddie Mac Variable Rate Debt Mortgages [Member] Secured Debt [Member]		Aug. 07, 2013 Minimum [Member] $500 million unsecured revolving credit faciltiy [Member] [Member] Unsecured Debt [Member]	Aug. 07, 2013 Maximum [Member] $500 million unsecured revolving credit faciltiy [Member] [Member] Unsecured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate									1.30%																							0.90%	1.70%
Unsecured notes payable	$ 810,000	$ 483,000
Total Outstanding Debt	$ 1,860,000	$ 1,670,000				$ 1,050,202	[1]	$ 810,000			$ 150,000	$ 310,000	$ 259,000	$ 382,817	$ 691,817	$ 350,000			$ 15,200	[1]	$ 358,385	[1]	$ 50,000	$ 189,721	[1]	$ 89,217	[1]	$ 64,247	[1]
Effective Rate	3.20%		2.70%	3.50%	[1]					4.90%	2.40%	4.50%	5.30%	4.70%		1.30%	0.90%	[1]	3.60%	[1]			4.70%	0.70%	[1]	0.90%	[1]	0.70%	[1]
Contract Maturity	Aug. 11, 2018		Jan. 14, 2019	Apr. 12, 2018	[1]					May 04, 2017	Mar. 01, 2017	Jul. 27, 2021	Jul. 20, 2014	Mar. 29, 2019		Aug. 07, 2017	Feb. 03, 2020	[1]					Mar. 31, 2017	Dec. 02, 2016	[1]	Jul. 23, 2031	[1]	Jul. 01, 2014	[1]	Jan. 01, 2016	[1]

[1] Includes capped balances.