Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Asset Retirement Obligation (Details)

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Summary of Significant Accounting Policies - Asset Retirement Obligation (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Asset Retirement Obligation    
Beginning balance $ 4,094 $ 3,700
Accretion expense 287 232
Foreign exchange impact (157) 162
Ending balance $ 4,224 $ 4,094