Debt Structure (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Total Outstanding Debt	$ 3,430,014	$ 3,470,000
Effective Rate	3.70%
Contract Maturity	Nov. 14, 2019
Secured Debt [Member]
Debt Instrument [Line Items]
Total Outstanding Debt	1,554,592
Effective Rate	3.40%
Contract Maturity	May 27, 2019
Secured Debt [Member] | Fixed Rate Debt
Debt Instrument [Line Items]
Total Outstanding Debt	1,215,496
Effective Rate	4.10%
Contract Maturity	Jan. 01, 2019
Secured Debt [Member] | Fixed Rate Debt | Individual property mortgages
Debt Instrument [Line Items]
Total Outstanding Debt	1,090,496
Effective Rate	4.00%
Contract Maturity	May 05, 2019
Secured Debt [Member] | Fixed Rate Debt | FNMA conventional credit facilities | 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 | LIBOR-based interest rate swaps
Debt Instrument [Line Items]
Total Outstanding Debt	75,000
Effective Rate	4.80%
Contract Maturity	Mar. 31, 2015
Secured Debt [Member] | Variable Rate Debt
Debt Instrument [Line Items]
Total Outstanding Debt	339,096
Effective Rate	1.00%
Contract Maturity	Nov. 02, 2020
Secured Debt [Member] | Variable Rate Debt | FNMA conventional credit facilities | FNMA
Debt Instrument [Line Items]
Total Outstanding Debt	221,585
Effective Rate	0.70%
Contract Maturity	Jan. 27, 2017
Secured Debt [Member] | Variable Rate Debt | FNMA tax-free credit facilities | FNMA
Debt Instrument [Line Items]
Total Outstanding Debt	90,415
Effective Rate	0.90%
Contract Maturity	Jul. 23, 2031
Secured Debt [Member] | Variable Rate Debt | Freddie Mac mortgages | Freddie Mac
Debt Instrument [Line Items]
Total Outstanding Debt	27,096
Effective Rate	3.40%
Contract Maturity	Oct. 31, 2015
Unsecured Debt [Member]
Debt Instrument [Line Items]
Total Outstanding Debt	1,875,422
Effective Rate	4.00%
Contract Maturity	Sep. 24, 2020
Unsecured Debt [Member] | Fixed Rate Debt | Term loans fixed with swaps
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
Debt Instrument [Line Items]
Total Outstanding Debt	$ 1,325,422
Effective Rate	4.50%
Contract Maturity	Dec. 03, 2021