Stock Offering Stock Offering (Textual) (Details) (USD $)	1 Months Ended	3 Months Ended	12 Months Ended			21 Months Ended
	Apr. 30, 2011	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012
Stock Offering [Abstract]
Sale of common stock shares	$ 125,000,000		$ 125,000,000
Number of shares sold under sales agreement		572,510				572,510
Proceeds from issuance of common stock under secondary security offering		$ 10,300,000	$ 10,283,000	$ 0	$ 0