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Gas Reserves (Tables)
 12 Months Ended
Dec. 31, 2018
Gas Reserves [Abstract]  
Gas Reserves Table [Text Block]
The following table outlines NW Natural's net gas reserves investment at December 31:
In thousands
 
2018
 
2017
Gas reserves, current
 
$
16,647

 
$
15,704

Gas reserves, non-current
 
170,660

 
171,832

Less: Accumulated amortization
 
104,463

 
87,779

Total gas reserves(1)
 
82,844

 
99,757

Less: Deferred taxes on gas reserves
 
20,071

 
22,712

Net investment in gas reserves
 
$
62,773

 
$
77,045


(1)
The net investment in additional wells included in total gas reserves was $4.8 million and $5.8 million at December 31, 2018 and 2017, respectively.