v3.19.3.a.u2

ALLOWANCE FOR DOUBTFUL ACCOUNTS (Tables) | 12 Months Ended
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Dec. 31, 2019
Accounts Receivable Additional Disclosures [Abstract] |
Allowance for Doubtful Accounts [Table Text Block] | The changes in the allowance for doubtful accounts consisted of the following:
| Year Ended December 31,
| 2019 |  | 2018 |  | 2017
| (Thousands of Dollars)
Balance as of beginning of year | $ | 9,412 |  |  | $ | 9,380 |  |  | $ | 7,700 |
Increase in allowance, net | 2,322 |  |  | 233 |  |  | 1,705 |
Accounts charged against the allowance | (11,662 | ) |  | (201 | ) |  | (25 | )
Balance as of end of year | $ | 72 |  |  | $ | 9,412 |  |  | $ | 9,380 |

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