Debt Structure (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Total Outstanding Debt	$ 3,475,413	$ 3,470,000
Effective Rate	3.80%
Contract Maturity	Sep. 29, 2019
Secured Debt [Member]
Debt Instrument [Line Items]
Total Outstanding Debt	1,563,014
Effective Rate	3.60%
Contract Maturity	Apr. 26, 2019
Secured Debt [Member] | Fixed Rate Debt
Debt Instrument [Line Items]
Total Outstanding Debt	1,276,194
Effective Rate	4.20%
Contract Maturity	Nov. 06, 2018
Secured Debt [Member] | Fixed Rate Debt | Individual Property Mortgages [Member]
Debt Instrument [Line Items]
Total Outstanding Debt	1,101,194
Effective Rate	4.00%
Contract Maturity	May 13, 2019
Secured Debt [Member] | Fixed Rate Debt | Conventional Credit Facility [Member] | FNMA
Debt Instrument [Line Items]
Total Outstanding Debt	50,000
Effective Rate	4.70%
Contract Maturity	Mar. 31, 2017
Secured Debt [Member] | Fixed Rate Debt | L I B O R [Member]
Debt Instrument [Line Items]
Total Outstanding Debt	125,000
Effective Rate	5.30%
Contract Maturity	Dec. 24, 2014
Secured Debt [Member] | Variable Rate Debt
Debt Instrument [Line Items]
Total Outstanding Debt	286,820
Effective Rate	1.00%
Contract Maturity	May 26, 2021
Secured Debt [Member] | Variable Rate Debt | Conventional Credit Facility [Member] | FNMA
Debt Instrument [Line Items]
Total Outstanding Debt	171,785
Effective Rate	0.70%
Contract Maturity	Jan. 31, 2017
Secured Debt [Member] | Variable Rate Debt | Tax Free Credit Facility [Member] | FNMA
Debt Instrument [Line Items]
Total Outstanding Debt	87,858
Effective Rate	0.90%
Contract Maturity	Jul. 22, 2031
Secured Debt [Member] | Variable Rate Debt | Mortgages [Member] | Freddie Mac
Debt Instrument [Line Items]
Total Outstanding Debt	27,177
Effective Rate	3.40%
Contract Maturity	Oct. 31, 2015
Unsecured Debt [Member]
Debt Instrument [Line Items]
Total Outstanding Debt	1,912,399
Effective Rate	4.00%
Contract Maturity	Sep. 03, 2020
Unsecured Debt [Member] | Fixed Rate Debt | Term Fixed Loan With Swaps [Member]
Debt Instrument [Line Items]
Total Outstanding Debt	550,000
Effective Rate	3.10%
Contract Maturity	Nov. 10, 2017
Unsecured Debt [Member] | Fixed Rate Debt | Senior Notes [Member]
Debt Instrument [Line Items]
Total Outstanding Debt	1,327,399
Effective Rate	4.50%
Contract Maturity	Dec. 03, 2021
Unsecured Debt [Member] | Variable Rate Debt | Variable Rate Credit Facility [Member]
Debt Instrument [Line Items]
Total Outstanding Debt	$ 35,000
Effective Rate	1.30%
Contract Maturity	Aug. 07, 2017