Equity and Capital Equity and Capital - Common Stock (Details) (USD $)	3 Months Ended		0 Months Ended	3 Months Ended
	Mar. 31, 2013	Aug. 10, 2012 Maximum	Apr. 03, 2013 Subsequent Event [Member]	Mar. 31, 2013 Restricted Stock [Member]
Class of Stock [Line Items]
Equity Issuances, Amount Available for Issuance	$ 75,600,000	$ 150,000,000
Common Stock, Shares, Issued	995,728		207,000
Weighted Average Price Per Share	$ 52.62		$ 52.45
Net proceeds from common stock issuance	51,600,000		10,700,000
Payments for Commission Expense	786,600
Payments of Stock Issuance Costs	$ 3,500
Shares granted (in shares)				230,000,000
Weighted average grant date fair value (in dollars per share)				$ 52.40