Amounts Reclassified Out of Accumulated Other Comprehensive Income - Additional Information (Detail) (Accumulated Other Comprehensive Income Pre Tax [Member], USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
	Mar. 31, 2013	Mar. 31, 2013
Accumulated Other Comprehensive Income Pre Tax [Member]
Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified out of AOCI pre tax basis	$ 0.3	$ 0.3