Accounts Receivable, Net and Revenue Concentrations

9 Months Ended

Sep. 30, 2019

Accounts receivable, net were as follows:



(In thousands)	September 30, 2019			December 31, 2018
Trade receivables, gross	$	151,220		$	133,774
Allowance for doubtful accounts	(1,292		)	(1,121		)
Allowance for sales returns	(497		)	(731		)
Net trade receivables	149,431			131,922
Other	7,707			12,767
Accounts receivable, net	$	157,138		$	144,689

Allowance for Doubtful Accounts

Changes in the allowance for doubtful accounts were as follows:



(In thousands)	Nine Months Ended September 30,
(In thousands)	2019			2018
Balance at beginning of period	$	1,121		$	1,064
Additions to costs and expenses	275			2
(Write-offs)/Foreign exchange effects	(104		)	(74		)
Balance at end of period	$	1,292		$	992

Significant Customers

Net sales to the following customers totaled more than 10% of our net sales:



	Three Months Ended September 30,
	2019				2018
	$ (thousands)		% of Net Sales		$ (thousands)			% of Net Sales
Comcast Corporation	$	30,419	15.2	%	$	32,336		17.7	%
Ring L.L.C.	$	21,050	10.5	%	—		⁽¹⁾	—		⁽¹⁾

⁽¹⁾ Net sales to this customer did not total more than 10% of our total net sales in the prior period.

There were no customers with an accounts receivable balance in excess of 10% of the total accounts receivable balance as of September 30, 2019.

Revenue Recognition Pattern

The pattern of revenue recognition was as follows:



	Three Months Ended September 30,				Nine Months Ended September 30,
(In thousands)	2019		2018		2019		2018
Goods and services transferred at a point in time	$	108,065	$	97,952	$	309,841	$	275,552
Goods and services transferred over time	92,659		84,765		268,942		234,386
Net sales	$	200,724	$	182,717	$	578,783	$	509,938