Condensed Consolidated Statement of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Condensed Consolidated Statement of Other Comprehensive Income (Loss) [Abstract]
Net income	$ 22.7	$ 11.0	$ 15.8	$ 17.3
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustment	(1.6)	0.7	(3.8)	(0.2)
Other comprehensive income (loss)	(1.6)	0.7	(3.8)	(0.2)
Comprehensive income	$ 21.1	$ 11.7	$ 12.0	$ 17.1