REVOLVING CREDIT FACILITIES AND TERM LOANS - Additional Information (Detail) (USD $)				9 Months Ended				9 Months Ended			1 Months Ended	9 Months Ended
	Sep. 30, 2012	Jan. 31, 2012	Dec. 31, 2011	Sep. 30, 2012 Unsecured Revolving Credit Facility Arranged by JP Morgan Securities, LLC and Wells Fargo Securities,LLC [Member]	Sep. 30, 2012 Euro Borrowings [Member]	Sep. 30, 2012 Canadian Borrowings [Member]	Sep. 30, 2012 Unsecured revolving credit facility with PNC Bank N.A. [Member]	Sep. 30, 2012 Revolving Credit Facilities [Member]	Sep. 30, 2012 Unsecured Term Loan - Tranche 1 [Member]	Jan. 31, 2012 Unsecured Term Loan - Tranche 1 [Member]	Aug. 31, 2012 Unsecured Term Loan- Tranche 2 [Member]	Sep. 30, 2012 Unsecured Term Loan- Tranche 2 [Member]	Jan. 31, 2012 Unsecured Term Loan- Tranche 2 [Member]
Debt Instrument [Line Items]
Unsecured revolving credit facility borrowing capacity				$ 750,000,000
Accordion feature				1,250,000,000
Line of Credit Facility competitive bid option on periodic interest rates				Up to 50% of the facility
Facility Fee				0.35%
Carrying Value				169,800,000	6,100,000	61,700,000	40,000,000
Unsecured revolving credit facility							65,000,000
Specified spread line of credit facility libor rate								1.65%
Specified spread line of credit facility prime rate								0.65%
Revolving Credit Facilities, Covenant Compliance								The Company was in compliance with these covenants at September 30, 2012.
Unsecured term loan	250,000,000	250,000,000	0						50,000,000	50,000,000		200,000,000	200,000,000
Term loan maturity date									Jan. 31, 2017			Jan. 31, 2019
Exercise of Accordion Feature											100,000,000
Undrawn amount												$ 100,000,000
Specified spread term loan Libor rate									1.70%			2.10%
Term Loan, Covenant Compliance									Company is in compliance with the covenants for Tranche 1 of the unsecured term loan.			Company is in compliance with the covenants for Tranche 2 of the unsecured term loan.