

Note 7.	Allowance for Doubtful Accounts Receivable and Sales Returns

Activity in the allowance for doubtful accounts receivable (in thousands):



	Years ended December 31,
	2018			2017			2016
Balance, beginning of year	$	725		$	633		$	765
Addition (reduction) to allowance	(224		)	(14		)	36
Amounts written off	—			—			(152		)
Effects of foreign currency translation	(26		)	106			(16		)
Balance, end of year	$	475		$	725		$	633

Activity in the allowance for sales returns (in thousands):



	Years ended December 31,
	2018			2017			2016
Balance, beginning of year	$	212		$	169		$	158
Addition (reduction) to allowance	(126		)	55			15
Amounts written off	—			(11		)	(3		)
Effects of foreign currency translation	(1		)	(1		)	(1		)
Balance, end of year	$	85		$	212		$	169
Total, Allowance for Doubtful Accounts Receivable and Sales Returns	$	560		$	937		$	802

Three customers individually comprised more than 10% of trade accounts receivable at December 31, 2018, with the customers accounting for 23%, 11% and 10% each. One customer accounted for 20% of our trade accounts receivable as of December 31, 2017.

One customer accounted for 11%, or $7.7 million, of consolidated revenue during the year ended December 31, 2018, in our Mobile Services segment.

One customer accounted for 10%, or $8.0 million, of consolidated revenue during the year ended December 31, 2017, which was reflected in our Mobile Services segment.

One customer accounted for 11%, or $9.1 million, of our consolidated revenue during the year ended December 31, 2016, in our Mobile Services segment.