Dividend Reinvestment and Stock Purchase Plan (Details) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	6 Months Ended		39 Months Ended
	Jun. 30, 2014	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014
Dividend Reinvestment and Stock Purchase Plan
Authorized common shares to be issued		6,000,000
Number of common shares issued	1,135,897	1,240,305	44,549	2,804,647
Amount raised from shares issued	$ 50.0	$ 54.4	$ 2.0	$ 114.5