Indebtedness - Schedule of Indebtedness (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2012
Unsecured Bank Term Loan [Member]
Debt Instrument [Line Items]
Debt instrument, Maturity Date	2018
Effective blended interest rate	3.24%
Secured Mortgage Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, Maturity Date	2015
Secured Mortgage Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, Maturity Date	2019
Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument, Maturity Date	2013
Senior Unsecured Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, Maturity Date	2017
Senior Unsecured Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, Maturity Date	2022