Income Tax Expense (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012	Mar. 31, 2011
Income Tax Expense [Abstract]
Effective income tax rate	38.60%	37.20%	38.20%	34.70%
Impact on income tax expense by write-down of a purchase accounting deferred asset			$ 0.5
Increase in effective tax rate	3.20%		2.10%
Impact on income tax expense by net research tax credits				0.4
Decrease in effective tax rate				1.20%
Estimated annual effective income tax rate			35.00%
Reduction in the amount of unrecognized tax benefits in the next twelve months	$ 1.8		$ 1.8