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Derivative Instruments (Schedule of Natural Gas Derivative Positions) (Details) - Natural Gas Derivative Positions [Member]
Mar. 31, 2017
MMBTU / d
$ / MMBTU
Swaps [Member] | FY 2017  
Derivative [Line Items]  
Derivative, Nonmonetary Notional Amount | MMBTU / d 20,000
Weighted Average Floor Price ($/MMBtu) | $ / MMBTU 3.30
Call Option [Member] | FY 2017  
Derivative [Line Items]  
Derivative, Nonmonetary Notional Amount | MMBTU / d 33,000
Weighted Average Ceiling Price ($/MMBtu) | $ / MMBTU 3.00
Call Option [Member] | FY 2018 [Member]  
Derivative [Line Items]  
Derivative, Nonmonetary Notional Amount | MMBTU / d 33,000
Weighted Average Ceiling Price ($/MMBtu) | $ / MMBTU 3.25
Call Option [Member] | FY 2019 [Member]  
Derivative [Line Items]  
Derivative, Nonmonetary Notional Amount | MMBTU / d 33,000
Weighted Average Ceiling Price ($/MMBtu) | $ / MMBTU 3.25
Call Option [Member] | FY 2020 [Member]  
Derivative [Line Items]  
Derivative, Nonmonetary Notional Amount | MMBTU / d 33,000
Weighted Average Ceiling Price ($/MMBtu) | $ / MMBTU 3.50