Common Shares (Tables)

9 Months Ended

Sep. 30, 2011

2010 ATM Program [Member]

Activity Under At-The-Market Share Offering Program

	Three Months Ended September 30, 2011		Nine Months Ended September 30, 2011
Total net consideration	$	—	$	13,847.0
Common shares sold		—		252.5
Average price per share	$	—	$	55.81

2011 ATM Program [Member]

Activity Under At-The-Market Share Offering Program

	Three Months Ended September 30, 2011		Nine Months Ended September 30, 2011
Total net consideration	$	32,736.8	$	56,015.9
Common shares sold		506.2		875.4
Average price per share	$	65.76	$	65.24