Dividend Reinvestment and Stock Purchase Plan (Details) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	12 Months Ended			34 Months Ended
	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013
Dividend Reinvestment and Stock Purchase Plan
Authorized common shares to be issued		6,000,000
Number of common shares issued	1,308,490	1,449,139	55,598	59,605	1,564,342
Amount raised from shares issued	$ 49.7	$ 55.6	$ 2.2	$ 2.0	$ 59.8