| Accounts receivable, net |
| | | | | | | | | | | December 31, 2018 | | | December 31, 2017 | | Accounts receivable | | $ | 76,376 | | | $ | 80,037 | | Less: provision for doubtful receivables | | | (16,086) | | | | (19,706) | | Accounts receivable, net | | $ | 60,290 | | | $ | 60,331 | | | | | | | | | | |
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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, 2016 | | $ | (18,278 | ) | | $ | (1,304 | ) | | $ | 145 | | | $ | (19,437 | ) | Year ended December 31, 2017 | | $ | (19,437 | ) | | $ | (269 | ) | | $ | — | | | $ | (19,706 | ) | Year ended December 31, 2018 | | $ | (19,706 | ) | | $ | (575 | ) | | $ | 4,195 | | | $ | (16,086 | ) |
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