Forward Equity Sales - Narrative (Details) (Forward Contracts [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Sep. 30, 2013	Oct. 31, 2013 Subsequent Event [Member]
Derivative [Line Items]
Forward equity authorized amount	$ 400.0
Average forward price	121.37	185.13	185.98
Notional amount	147.2	37.6	39.4
Notional amount settled		$ 77.0
Average forward price total		185.56