

Note 6.	Allowance for Doubtful Accounts Receivable and Sales Returns

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



	Years ended December 31,
	2016			2015			2014
Balance, beginning of year	$	765		$	1,288		$	966
Addition (reduction) to allowance	36			(355		)	433
Amounts written off	(152		)	(77		)	—
Effects of foreign currency translation	(16		)	(91		)	(111		)
Balance, end of year	$	633		$	765		$	1,288

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



	Years ended December 31,
	2016			2015			2014
Balance, beginning of year	$	158		$	354		$	569
Addition (reduction) to allowance	15			(186		)	(209		)
Amounts written off	(3		)	(9		)	(6		)
Effects of foreign currency translation	(1		)	(1		)	—
Balance, end of year	$	169		$	158		$	354
Total, Allowance for Doubtful Accounts Receivable and Sales Returns	$	802		$	923		$	1,642

One customer accounted for 64% of trade accounts receivable at December 31, 2016. One customer accounted for 52% and one other customer accounted for 12% of trade accounts receivable as of December 31, 2015.

One customer accounted for 32% or $38.9 million, of consolidated revenue during the year ended December 31, 2016, in our Mobile Services segment.

One customer accounted for 26%, or $32.9 million, of consolidated revenue during the year ended December 31, 2015, which is reflected in our Mobile Services segment.

One customer accounted for 20%, or $31.9 million, of consolidated revenue during the year ended December 31, 2014, which is reflected in our Mobile Services segment.