Share-Based Employee Compensation - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended				1 Months Ended		6 Months Ended	3 Months Ended		6 Months Ended		1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended			1 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Aug. 07, 2013	Aug. 07, 2013 Stock Awards [Member]	Aug. 31, 2013 Fiscal 2014 Employee Stock Option Grant [Member]	Aug. 31, 2013 Fiscal 2014 Board of Directors Grant [Member]	Sep. 30, 2013 Stock Options [Member]	Sep. 30, 2013 Restricted Stock Units (RSUs) [Member]	Sep. 30, 2012 Restricted Stock Units (RSUs) [Member]	Sep. 30, 2013 Restricted Stock Units (RSUs) [Member]	Sep. 30, 2012 Restricted Stock Units (RSUs) [Member]	Aug. 31, 2013 Restricted Stock [Member]	Sep. 30, 2013 Restricted Stock [Member]	Sep. 30, 2012 Restricted Stock [Member]	Sep. 30, 2013 Restricted Stock [Member]	Sep. 30, 2012 Restricted Stock [Member]	Mar. 31, 2013 Restricted Stock [Member]	Mar. 31, 2013 Restricted Stock [Member] Minimum [Member]	Mar. 31, 2013 Restricted Stock [Member] Maximum [Member]	Aug. 31, 2013 Restricted Stock [Member] Board of Directors [Member]
Share Based Employee Compensation [Line Items]
Number of shares available for future grant	3,973,459		3,973,459		3,000,000	1,500,000
Number of shares granted			236,989				206,914	30,075
Share-based compensation vesting period							3 years												5 years
Share-based compensation award expiration term							10 years	10 years
Stock option expense	$ 1.9	$ 1.3	$ 2.7	$ 1.8
Unrecognized compensation cost, stock options									10.3
Weighted-average period of recognition of unrecognized compensation cost									2 years 4 months 24 days								3 years 8 months 12 days
Aggregate intrinsic value for outstanding options	103.3		103.3
Aggregate intrinsic value of exercisable options	37.7		37.7
Total intrinsic value of options exercised			2.9
Restricted stock or unit expense										0	0.4	0	0.8		1.2	0.9	2.1	1.6
Number of shares granted														93,186								5,761
Percentage of average return on invested capital																				15.00%
Period of average return on invested capital exceeded target																			10 years
Share-based compensation vesting date																				Mar. 31, 2015	Mar. 31, 2017
Unrecognized compensation cost															$ 17.7		$ 17.7