Income Taxes - NOL and Capital Loss Carryforwards (Details) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Income tax
Effective income tax rate (as a percent)	39.00%	39.00%
Income tax benefit for discrete items	$ 0.2	$ 3.0
Net operating and capital loss carryforwards	34.1
Tax credit carryforwards	$ 27.7
Minimum
Income tax
Operating loss carryforwards expiration date	Sep. 30, 2017
Tax credit carryforwards, expiration date	Sep. 30, 2025
Maximum
Income tax
Operating loss carryforwards expiration date	Sep. 30, 2037
Tax credit carryforwards, expiration date	Sep. 30, 2037