Income Taxes - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2018	Mar. 31, 2018	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Decrease in valuation allowance	$ 46.2
Benefit related to re-measurement of deferred tax liabilities				$ 0.7
U.S. statutory federal tax rate (as a percent)	21.00%	35.00%	21.00%
Reductions in unrecognized tax benefits from expiration					$ 0.7
Cumulative effect adjustment to retained earnings				$ 4.0
Toll charge, payable period				8 years
Toll charge, estimated foreign earnings	$ 120.0			$ 120.0
Toll charge, estimated foreign earnings, provision amount, unrecorded				$ 5.2
U.S. statutory federal tax rate, prorated allocation (as a percent)	24.50%			24.50%
Anticipated unrecognized tax benefit reduction during next twelve months	$ 0.2			$ 0.2