Plant and Equipment, Net (Narrative) (Details) $ in Millions	1 Months Ended	3 Months Ended								12 Months Ended
	Jan. 31, 2016 USD ($) plant	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)
Property, Plant and Equipment [Abstract]
Depreciation expense										$ 39.4	$ 48.1	$ 48.3
Long Lived Assets Held-for-sale [Line Items]
Income tax provision		$ 15.6	$ 17.6	$ 12.2	$ 13.4	$ 3.6	$ 10.8	$ 11.2	$ 6.1	$ 58.8	$ 31.7	$ 31.9
Onsite Ammonia Plant
Long Lived Assets Held-for-sale [Line Items]
Number of plants sold | plant	2
Proceeds from sale of plants	$ 17.1			17.1
Gain from sale of plants				1.4
Income tax provision				$ 1.5