Equity Financing - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	0 Months Ended		1 Months Ended	2 Months Ended	9 Months Ended	12 Months Ended
	Apr. 30, 2014	Jul. 31, 2013	Jan. 31, 2013	Oct. 31, 2012	Sep. 30, 2013	Dec. 31, 2012	Apr. 30, 2014
Equity [Abstract]
Common stock issued	2,700,000		87,000	2,000,000	3,400,000	4,900,000
Common stock average price per share						$ 25.25	$ 38.00
Net proceeds from issue of common stock	$ 94.5		$ 2.1	$ 36.2	$ 123.0	$ 118.1
Common stock shares to be sold at market prices		$ 125.0