Accounts receivable, less the allowance for doubtful accounts, represents the net amount expected to be collected. Assessing the collectability of the receivables (billed and unbilled) requires management judgment based on a combination of factors, including but not limited to, an evaluation of our historical incurred loss experience, credit-worthiness of our clients, age of the trade receivable balance, current economic conditions that may affect a client’s ability to pay, and reasonable and supportable forecasts. Receivables are charged-off against the allowance when the balance is deemed uncollectible.

We considered the impact of the COVID-19 pandemic, the resulting macroeconomic conditions, client’s location, industry, and financial position in our estimation of the allowance for doubtful accounts. During the nine month period ended September 30, 2020, we recorded bad debt expense due to the COVID-19 pandemic of $2.2 million. We did not recognize any bad debt expense related to the COVID-19 pandemic for the three month period ended September 30, 2020.

Accounts receivable, net, at September 30, 2020 and December 31, 2019 were as follows (in thousands):

	September 30,			December 31,
	2020			2019
Trade accounts receivable	$	173,980		$	176,375
Unbilled revenue, at net realizable value		89,851			60,035
Total accounts receivable		263,831			236,410
Allowance for doubtful accounts		(14,945	)		(14,379	)
Accounts receivable, net	$	248,886		$	222,031

Changes to the allowance for doubtful accounts for the nine months ended September 30, 2020 are as follows (in thousands):

	September 30,
	2020
Balance at beginning of period	$	(14,379	)
Provision for losses		(6,658	)
Charge-offs, net of recoveries		6,092
Allowance for doubtful accounts	$	(14,945	)