pre_text: Accounts Receivable and Allowance for Doubtful Accounts Accounts receivable consists primarily of amounts due to the Company from normal business activities. We maintain an allowance for doubtful accounts for estimated losses that result from the inability of our customers to make required payments. The allowance for doubtful accounts is maintained based on customer payment levels, historical experience and management’s views on trends in the overall receivable agings. In addition, for larger accounts, we perform analyses of risks on a customer-specific basis. We perform ongoing credit evaluations of our customers’ financial condition and management believes that an adequate allowance for doubtful accounts has been provided. Uncollectible accounts are removed from accounts receivable and are charged against the allowance for doubtful accounts when internal collection efforts have been unsuccessful. The following table summarizes the activity in allowance for doubtful accounts for the years ended December 31, 2019, 2018 and 2017:
table: Year Ended December 31,
table: (In thousands) 2019 2018 2017
table: Balance at beginning of year $4,421 $6,667 $2,813
table: Provision charged to expense 9,347 8,793 7,072
table: Write-offs, less recoveries (9,219) (11,039) (6,516)
table: Acquired allowance for doubtful accounts — — 3,298
table: Balance at end of year $4,549 $4,421 $6,667
question: Analyse this data from a financial earnings document. What was the average provision charged to expense for 2017-2019?