Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Foreign currency (Details)

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Summary of Significant Accounting Policies - Foreign currency (Details) - USD ($)
$ in Thousands
 6 Months Ended 12 Months Ended
Dec. 31, 2015
Dec. 31, 2017
Dec. 31, 2016
Jun. 30, 2015
Other income , net        
Foreign currency transaction gain $ 12,596 $ 8,744 $ 1,002 $ 11,200