Goodwill and Intangible Assets, Net (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended 9 Months Ended
Sep. 30, 2014
Sep. 30, 2013
Sep. 30, 2014
Sep. 30, 2013
Dec. 31, 2013
Finite-Lived Intangible Assets [Line Items]          
Gross intangible asset $ 90.9   $ 90.9   $ 62.6
Accumulated amortization (16.6)   (16.6)   (13.7)
Net intangible assets 74.3   74.3   48.9
Amortization expense 1.3 0.5 3.1 1.5  
Acquired Indefinite-lived Intangible Assets [Line Items]          
Goodwill 71.0   71.0   20.5
Wolf Trax, Inc. [Member]
         
Acquired Indefinite-lived Intangible Assets [Line Items]          
Additional goodwill due to Wolf Trax     51.9    
Water Rights [Member]
         
Acquired Indefinite-lived Intangible Assets [Line Items]          
Indefinite-lived intangible assets 22.9   22.9   22.9
Trade Names [Member]
         
Acquired Indefinite-lived Intangible Assets [Line Items]          
Indefinite-lived intangible assets 12.8   12.8   0.7
Plant Nutrition [Member]
         
Acquired Indefinite-lived Intangible Assets [Line Items]          
Goodwill 64.3   64.3   13.8
Supply Agreement
         
Finite-Lived Intangible Assets [Line Items]          
Average useful life     50 years    
Gross intangible asset 32.5   32.5   34.1
Accumulated amortization (2.5)   (2.5)   (2.0)
Net intangible assets 30.0   30.0   32.1
SOP Production Rights [Member]
         
Finite-Lived Intangible Assets [Line Items]          
Average useful life     25 years    
Gross intangible asset 24.3   24.3   24.3
Accumulated amortization (10.5)   (10.5)   (9.8)
Net intangible assets 13.8   13.8   14.5
Customer and distributor relationships [Member]
         
Finite-Lived Intangible Assets [Line Items]          
Gross intangible asset 8.8   8.8   2.1
Accumulated amortization (2.2)   (2.2)   (1.8)
Net intangible assets 6.6   6.6   0.3
Customer and distributor relationships [Member] | Minimum [Member]
         
Finite-Lived Intangible Assets [Line Items]          
Average useful life     5 years    
Customer and distributor relationships [Member] | Maximum [Member]
         
Finite-Lived Intangible Assets [Line Items]          
Average useful life     10 years    
Developed technology [Member]
         
Finite-Lived Intangible Assets [Line Items]          
Average useful life     5 years    
Lease Rights [Member]
         
Finite-Lived Intangible Assets [Line Items]          
Average useful life     25 years    
Gross intangible asset 2.0   2.0   2.1
Accumulated amortization (0.2)   (0.2)   (0.1)
Net intangible assets 1.8   1.8   2.0
Trademarks [Member]
         
Finite-Lived Intangible Assets [Line Items]          
Average useful life     10 years    
Patents [Member]
         
Finite-Lived Intangible Assets [Line Items]          
Gross intangible asset 18.5   18.5    
Accumulated amortization (0.8)   (0.8)    
Net intangible assets 17.7   17.7    
Patents [Member] | Minimum [Member]
         
Finite-Lived Intangible Assets [Line Items]          
Average useful life     10 years    
Patents [Member] | Maximum [Member]
         
Finite-Lived Intangible Assets [Line Items]          
Average useful life     20 years    
Noncompete Agreements [Member]
         
Finite-Lived Intangible Assets [Line Items]          
Average useful life     5 years    
Other [Member]
         
Finite-Lived Intangible Assets [Line Items]          
Gross intangible asset 4.8   4.8    
Accumulated amortization (0.4)   (0.4)    
Net intangible assets $ 4.4   $ 4.4