CONSOLIDATED STATEMENTS OF INCOME (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Net sales	$ 572.2	$ 473.6	$ 1,539.7	$ 1,289.9
Cost of sales	476.2	390.5	1,272.4	1,098.3
Gross profit	96.0	83.1	267.3	191.6
Selling, general and administrative expenses	50.8	47.3	139.6	139.0
Operating income	45.2	35.8	127.7	52.6
Interest expense	(7.5)	(7.7)	(22.0)	(22.5)
Other income, net	0.0	1.0	0.9	2.0
Income before income taxes	37.7	29.1	106.6	32.1
Income tax expense (benefit)	7.5	8.4	(39.1)	10.6
Net income	$ 30.2	$ 20.7	$ 145.7	$ 21.5
EARNINGS PER COMMON SHARE:
Basic (in dollars per share)	$ 0.63	$ 0.44	$ 3.06	$ 0.45
Diluted (in dollars per share)	$ 0.63	$ 0.44	$ 3.04	$ 0.45
WEIGHTED AVERAGE COMMON SHARES OUTSTANDING:
Basic (in shares)	47.2	47.0	47.2	47.0
Diluted (in shares)	47.7	47.1	47.5	47.1
Cash dividends per common share (in dollars per share)	$ 0.18	$ 0.18	$ 0.54	$ 0.54