v3.8.0.1

ALLOWANCE FOR DOUBTFUL ACCOUNTS | 12 Months Ended
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Dec. 31, 2017
Accounts Receivable Additional Disclosures [Abstract] |
ALLOWANCE FOR DOUBTFUL ACCOUNTS | ALLOWANCE FOR DOUBTFUL ACCOUNTS The changes in the allowance for doubtful accounts consisted of the following:
| Year Ended December 31,
| 2017 |  | 2016 |  | 2015
| (Thousands of Dollars)
Balance as of beginning of year | $ | 7,756 |  |  | $ | 8,473 |  |  | $ | 7,808 |
Increase in allowance, net | 2,217 |  |  | 24 |  |  | 965 |
Accounts charged against the allowance | (25 | ) |  | (741 | ) |  | (300 | )
Balance as of end of year | $ | 9,948 |  |  | $ | 7,756 |  |  | $ | 8,473 |

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- Definition The entire disclosure for allowance for credit losses. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -URI http://asc.fasb.org/topic&trid=2196771 + Details
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