Condensed Consolidated Statements of Equity - USD ($) $ in Millions	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income
Beginning balance (in shares) at Sep. 30, 2016		89,286,936	0
Beginning balance at Sep. 30, 2016	$ 744.8	$ 0.0	$ 0.0	$ 758.9	$ (9.6)	$ (4.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of restricted stock (in shares)		5,434
Forfeiture of restricted stock awards (in shares)		(10,753)
Shares associated with employee tax withholding for vesting of certain equity awards (in shares)		(9,576)	9,576
Shares associated with employee tax withholding for vesting of certain equity awards	(0.1)		$ (0.1)
Equity-based compensation	4.2			4.2
Comprehensive income:
Net income	0.8				0.8
Other comprehensive loss	4.5					4.5
Ending balance (in shares) at Jun. 30, 2017		89,272,041	9,576
Ending balance at Jun. 30, 2017	754.2	$ 0.0	$ (0.1)	763.1	(8.8)	0.0
Beginning balance (in shares) at Sep. 30, 2016		89,286,936	0
Beginning balance at Sep. 30, 2016	744.8	$ 0.0	$ 0.0	758.9	(9.6)	(4.5)
Ending balance (in shares) at Sep. 30, 2017		89,344,065	9,576
Ending balance at Sep. 30, 2017	777.6	$ 0.0	$ (0.1)	764.4	4.8	8.5
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of restricted stock (in shares)		415,867
Vesting of restricted stock units (in shares)		8,162
Forfeiture of restricted stock awards (in shares)		(24,008)
Shares associated with employee tax withholding for vesting of certain equity awards (in shares)		(9,940)	9,940
Shares associated with employee tax withholding for vesting of certain equity awards	(0.1)		$ (0.1)
Equity-based compensation	5.3			5.3
Comprehensive income:
Net income	44.4				44.4
Other comprehensive loss	(1.3)					(1.3)
Ending balance (in shares) at Jun. 30, 2018		89,734,146	19,516
Ending balance at Jun. 30, 2018	$ 825.9	$ 0.0	$ (0.2)	$ 769.7	$ 49.2	$ 7.2