Other Comprehensive Income of the Operating Partnership (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Other Comprehensive Income [Line Items]
Other Comprehensive Income, Foreign Currency Transaction and Translation Adjustment, before Tax	$ (2,200,000)	$ 3,700,000	$ (63,000)	$ (2,000,000)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	39,400,000	44,700,000	169,400,000	114,800,000
Liberty Property Limited Partnership [Member]
Other Comprehensive Income [Line Items]
Other Comprehensive Income, Foreign Currency Transaction and Translation Adjustment, before Tax	(2,200,000)	3,700,000	(63,000)	(2,000,000)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$ 39,400,000	$ 44,700,000	$ 169,400,000	$ 114,800,000