EARNINGS PER COMMON SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions		3 Months Ended								12 Months Ended
	Apr. 03, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Basic EPS:
Net income		$ (13.3)	$ 21.7	$ 108.0	$ 45.2	$ (14.2)	$ 10.7	$ 100.8	$ 46.9	$ 161.6	$ 144.2	$ 136.9
Less: Income allocated to participating securities										0.4	0.5	0.5
Net Income Available to Common Shareholders										$ 161.2	$ 143.7	$ 136.4
Weighted Average Shares Outstanding, Basic (in Shares)										46,900	44,100	43,200
Earnings Per Share of Common Stock (in dollars per share)		$ (0.28)	$ 0.45	$ 2.36	$ 0.99	$ (0.31)	$ 0.24	$ 2.32	$ 1.08	$ 3.44	$ 3.26	$ 3.16
Diluted EPS:
Net income		$ (13.3)	$ 21.7	$ 108.0	$ 45.2	$ (14.2)	$ 10.7	$ 100.8	$ 46.9	$ 161.6	$ 144.2	$ 136.9
Less: Income allocated to participating securities										0.4	0.5	0.5
Net Income Available to Common Shareholders										$ 161.2	$ 143.7	$ 136.4
Weighted Average Shares Outstanding, Basic (in Shares)										46,900	44,100	43,200
Dilutive Effect of Stock Options, Restricted Stock, and Restricted Stock Units (in shares)										100	200	100
Weighted Average Diluted Shares (in shares)										47,000	44,300	43,300
Earnings Per Share of Common Stock (in dollars per share)		$ (0.28)	$ 0.45	$ 2.36	$ 0.99	$ (0.31)	$ 0.24	$ 2.31	$ 1.08	$ 3.43	$ 3.24	$ 3.16
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding shares excluded from calculation of diluted EPS (in shares)	2,500									2,875
Restricted stock and stock units subject to performance and/or market conditions
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding shares excluded from calculation of diluted EPS (in shares)										500	300	300