DERIVATIVE INSTRUMENTS (Details)	Mar. 31, 2015 dts
Basis and Index Related Purchase and Sales Contracts
Derivative [Line Items]
Outstanding derivative contracts notional amount	315,300,000
Natural Gas (in MMdts) | Derivative Transaction Type, Purchase
Derivative [Line Items]
Outstanding derivative contracts notional amount	55,900,000
Natural Gas (in MMdts) | Derivative Transaction Type, Sale
Derivative [Line Items]
Outstanding derivative contracts notional amount	45,700,000
Electricity (in MMmwh) | Derivative Transaction Type, Purchase
Derivative [Line Items]
Outstanding derivative contracts notional amount	2,700,000
Electricity (in MMmwh) | Derivative Transaction Type, Sale
Derivative [Line Items]
Outstanding derivative contracts notional amount	2,700,000