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Gas Reserves (Tables)
 3 Months Ended
Mar. 31, 2017
Gas Reserves [Abstract]  
Gas Reserves Table [Text Block]
 
 
March 31,
 
December 31,
In thousands
 
2017
 
2016
 
2016
Gas reserves, current
 
$
15,378


$
16,420


$
15,926

Gas reserves, non-current
 
172,158

 
171,121

 
171,610

Less: Accumulated amortization
 
75,528

 
59,976

 
71,426

Total gas reserves(1)
 
112,008


127,565


116,110

Less: Deferred taxes on gas reserves
 
32,179

 
28,547

 
28,119

Net investment in gas reserves
 
$
79,829

 
$
99,018

 
$
87,991