Accounts Receivable

9 Months Ended

Sep. 30, 2018

Receivables [Abstract]

Accounts Receivable

3. Accounts Receivable

(Table only in thousands)	September 30, 2018			December 31, 2017
Contract receivables	$	62,787		$	60,543
Trade receivables		7,900			11,603
Allowance for doubtful accounts		(2,883	)		(4,156	)
Total accounts receivable	$	67,804		$	67,990

Balances billed but not paid by customers under retainage provisions in contracts within the Condensed Consolidated Balance Sheets amounted to approximately $1.3 million and $2.5 million at September 30, 2018 and December 31, 2017, respectively. Retainage receivables on contracts in progress are generally collected within a year after contract completion.

Bad debt expense was $0.6 million and $1.2 million for the three-month periods ended September 30, 2018 and 2017, respectively, and $1.2 million and $2.2 million for the nine-month periods ended September 30, 2018 and 2017, respectively.

The decrease in the allowance for doubtful accounts is primarily due to divested businesses and classification of the Zhongli balance to held for sale.