Indebtedness - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Debt Instrument [Line Items]
Letters of credit issued	$ 570
Net loss on extinguishment of indebtedness		(301)
Coverage's ratio	1.5
Company's ratio	2.0
Unencumbered assets to unsecured debt	1.5
Leverage ratio	60.00%
Total secured debt to total asset value	40.00%
Line of credit facility, covenant terms	The Company's Syndicated Line, Cash Management Line, Term Loan and senior unsecured notes contain customary restrictions, representations, covenants and events of default and require the Company to meet certain financial covenants. Debt service and fixed charge coverage covenants require the Company to maintain
Unsecured Bank Term Loan [Member]
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity	300,000
Interest Rate, spread over LIBOR	1.70%
Line of credit facility, expiration year	January 2018
Interest rate based on credit ratings ranges, maximum	2.30%
Interest rate based on credit ratings ranges, minimum	1.50%
Number of extension options	2
Time period for term loan extension option	6 months
Unsecured Bank Term Loan [Member] | Interest Rate Swap [Member]
Debt Instrument [Line Items]
Interest rate paid under the Term Loan	1.54%
Effective blended interest rate on the Term Loan	3.24%
Cash Management Line [Member]
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity	30,000
Line of credit facility, expiration year	January 2016
Number of extension options	1
Lines of Credit [Member]
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity	300,000
Interest Rate, spread over LIBOR	1.225%
Line of credit facility annual facility fees percentage	0.225%
Line of credit facility, expiration year	January 2016
Interest rate based on credit ratings ranges, minimum	1.00%
Interest rate based on credit ratings ranges, maximum	1.80%
Facility fee rate based on credit ratings range, minimum	0.15%
Facility fee rate based on credit ratings range, maximum	0.40%
Line of credit facility, competitive bid option for short-term funds, percentage	50.00%
Net loss on extinguishment of indebtedness		$ 301