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SCHEDULE II VALUATION AND QUALIFYING ACCOUNTS (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Allowance for Doubtful Accounts |  |  |
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |
Balance Beginning of Period | $ 22,493 | $ 26,368 | $ 16,173
Additions Charged to Operating Expense | 10,133 | 2,408 | 15,817
Deductions from Reserves | 7,992 | 6,283 | 5,622
Balance End of Period | 24,634 | 22,493 | 26,368
Revenue Allowance |  |  |
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |
Balance Beginning of Period | 16,218 | 17,947 | 11,626
Additions Charged to Operating Expense | 45,784 | 35,549 | 41,338
Deductions from Reserves | 41,887 | 37,278 | 35,017
Balance End of Period | 20,115 | 16,218 | 17,947
Valuation Allowance on Deferred Tax Assets |  |  |
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |
Balance Beginning of Period | 83,643 | 79,295 | 68,355
Additions Charged to Operating Expense | (11,339) | 4,459 | 10,466
Deductions from Reserves | 4,740 | (111) | 474
Balance End of Period | $ 77,044 | $ 83,643 | $ 79,295

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- Definition Amount of valuation and qualifying accounts and reserves. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-09(Column B)) -URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e24092-122690 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-09(Column E)) -URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e24092-122690 + Details
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