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Gas Reserves (Tables)
 12 Months Ended
Dec. 31, 2017
Gas Reserves [Abstract]  
Gas Reserves Table [Text Block]
In thousands
 
2017
 
2016
Gas reserves, current
 
$
15,704

 
$
15,926

Gas reserves, non-current
 
171,832

 
171,610

Less: Accumulated amortization
 
87,779

 
71,426

Total gas reserves(1)
 
99,757

 
116,110

Less: Deferred taxes on gas reserves
 
22,712

 
28,119

Net investment in gas reserves
 
$
77,045

 
$
87,991


(1)
Our net investment in additional wells included in total gas reserves was $5.8 million and $6.7 million at December 31, 2017 and 2016, respectively.