TRADE ACCOUNTS RECEIVABLE, NET OF ALLOWANCE

9 Months Ended

Sep. 30, 2015

TRADE ACCOUNTS RECEIVABLE, NET OF ALLOWANCE

6. TRADE ACCOUNTS RECEIVABLE, NET OF ALLOWANCE

(in thousands)	September 30, 2015			December 31, 2014
Trade accounts receivable	$	113,207		$	128,757
Unbilled trade accounts receivable		18,145			27,627
Total accounts receivable		131,352			156,384
Allowance for sales credit memos		(2,100	)		(1,540	)
	$	129,252		$	154,844

Unbilled trade accounts receivable primarily relate to services revenue earned under time and materials arrangements and to maintenance and license arrangements that have commenced or been delivered but have not been invoiced.