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Segment information (Tables)
12 Months Ended
Dec. 31, 2020
Segment Reporting [Abstract]  
Segment Information - Revenue by Geographic Region

 

    Year Ended
December 31,
2020
    Year Ended
December 31,
2019
    Year Ended
December 31,
2018
 
Asia $ 136,515   $ 119,344   $ 120,660  
Europe   71,531     95,542     86,633  
North America   18,576     3,118     17,862  
Australia   149     1,375     6,206  
Total $ 226,771   $ 219,379   $ 231,361