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UNEARNED REVENUE (Tables)
6 Months Ended
Jun. 30, 2021
Unearned Revenue  
Changes in unearned revenue

UNEARNED REVENUE
   Six Months Ended June 30, 
(in thousands)  2021   2020 
Balance at beginning of year  $149,224   $136,507 
Deferral of unearned revenue   116,034    105,928 
Recognition of unearned revenue   (92,307)   (85,936)
Balance at end of period  $172,951   $156,499