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Gas Reserves (Tables)
 3 Months Ended
Mar. 31, 2016
Gas Reserves [Abstract]  
Gas Reserves Table [Text Block]
 
 
March 31,
 
December 31,
In thousands
 
2016
 
2015
 
2015
Gas reserves, current
 
$
16,420

 
$
19,112

 
$
17,094

Gas reserves, non-current
 
171,121

 
168,352

 
170,453

Less: Accumulated amortization
 
59,976

 
43,165

 
55,901

Total gas reserves(1)
 
127,565

 
144,299

 
131,646

Less: Deferred taxes on gas reserves
 
28,547

 
28,383

 
27,203

Net investment in gas reserves(1)
 
$
99,018

 
$
115,916

 
$
104,443