Equity Financings - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended		9 Months Ended
	Jul. 03, 2013	Jan. 31, 2013	Sep. 30, 2013
Equity Financing [Abstract]
Common stock issued		87,000	3,400,000
Net proceeds from issue of common stock	$ 125.0	$ 2.1	$ 123.0