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