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Asset Retirement Obligation (Tables)
 6 Months Ended
Jun. 30, 2017
Asset Retirement Obligation [Abstract]  
Schedule of Asset Retirement Obligations [Table Text Block]
The following table presents a reconciliation of the beginning and ending aggregate carrying amounts of asset retirement obligation (in thousands):
 
 
Six months ended June 30,
 
 
2017
 
2016
Beginning asset retirement obligations
 
$
44,783

 
$
42,197

Net additions during the period (1)
 
5,994

 
—

Foreign currency translation adjustment
 
91

 
159

Accretion expense
 
1,357

 
1,260

Ending asset retirement obligations
 
$
52,225

 
$
43,616