| Accounts receivable, net |
| | December 31, 2017 | | December 31, 2016 | | Accounts receivable | | $ | 80,037 | | $ | 85,266 | | Less: provision for doubtful receivables | | | (19,706) | | | (19,437) | | Accounts receivable, net | | $ | 60,331 | | $ | 65,829 | |
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| Allowance for doubtfull receivables |
| | | | | | | | | | | | | Allowance for doubtful receivables | | Balance at Beginning of Period | | Charges to Costs and Expenses | | Amount Utilized | | Balance at End of Period | Year ended December 31, 2015 | | $ | (18,464) | | $ | (59) | | $ | 245 | | $ | (18,278) | Year ended December 31, 2016 | | $ | (18,278) | | $ | (1,304) | | $ | 145 | | $ | (19,437) | Year ended December 31, 2017 | | $ | (19,437) | | $ | (269) | | $ | — | | $ | (19,706) |
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