Annual report pursuant to Section 13 and 15(d)

Significant Accounting Policies - Schedule of Changes to Allowance for Doubtful Accounts (Details)

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Significant Accounting Policies - Schedule of Changes to Allowance for Doubtful Accounts (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Receivables [Abstract]      
Allowance for doubtful accounts, beginning of period $ 7,602 $ 2,490 $ 704
Additional provisions for the year 1,512 5,112 1,786
Allowance for doubtful accounts, end of period $ 9,114 $ 7,602 $ 2,490