| Accounts receivable, net |
| | December 31, 2019 | | | December 31, 2018 | | Accounts receivable | | $ | 68,309 | | | $ | 76,376 | | | Less: provision for doubtful receivables | | | (16,377) | | | | (16,086) | | | Accounts receivable, net | | $ | 51,932 | | | $ | 60,290 | | | | | | | | | | | | | | | | | | | | | | | |
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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, 2017 | | $ | (19,437 | ) | | $ | (269 | ) | | $ | — | | | $ | (19,706 | ) | Year ended December 31, 2018 | | $ | (19,706 | ) | | $ | (575 | ) | | $ | 4,195 | | | $ | (16,086 | ) | Year ended December 31, 2019 | | $ | (16,086 | ) | | $ | (999 | ) | | $ | 708 | | | $ | (16,377 | ) |
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