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Gas Reserves (Tables)
 6 Months Ended
Jun. 30, 2016
Gas Reserves [Abstract]  
Gas Reserves Table [Text Block]
 
 
June 30,
 
December 31,
In thousands
 
2016
 
2015
 
2015
Gas reserves, current
 
$
15,707

 
$
18,214

 
$
17,094

Gas reserves, non-current
 
171,834

 
169,288

 
170,453

Less: Accumulated amortization
 
63,548

 
47,933

 
55,901

Total gas reserves(1)
 
123,993

 
139,569

 
131,646

Less: Deferred taxes on gas reserves
 
26,737

 
27,357

 
27,203

Net investment in gas reserves(1)
 
$
97,256

 
$
112,212

 
$
104,443