Equity Offering (Details) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2012
Class of Stock [Line Items]
Proceeds from Issuance of Common Stock	$ 174,700,000	$ 174,720,000	$ 79,040,000
Common Stock [Member]
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues	5,175,000
Sale of Stock, Price Per Share	$ 35.40	$ 35.40
Stock Issuance Costs	$ 8,500,000