Our revenue performance obligations are primarily satisfied at a point in time and limited revenue streams are satisfied over time as work progresses.

The following is a summary of our revenue performance obligations in the three and nine months ended September 30, 2019 and the three and nine months ended September 30, 2018:


	Three Months Ended September 30, 2019				Three Months Ended September 30, 2018
(In thousands except percentages)	Revenues		Percent of Revenues		Revenues		Percent of Revenues
Revenue recognized over time	$	403	3	%	$	1,241	7	%
Revenue recognized at a point in time		11,988	97	%		15,442	93	%
	$	12,391	100	%	$	16,683	100	%


	Nine Months Ended September 30, 2019				Nine Months Ended September 30, 2018
(In thousands except percentages)	Revenues		Percent of Revenues		Revenues		Percent of Revenues
Revenue recognized over time	$	1,041	2	%	$	3,262	7	%
Revenue recognized at a point in time		41,370	98	%		43,395	93	%
	$	42,411	100	%	$	46,657	100	%

Contract assets consist of unbilled amounts from sales where we recognize the revenue over time and the revenue recognized exceeds the amount billed to the customer at a point in time. Accounts receivable are recorded when the right to payment becomes unconditional. Contract liabilities consist of payments received in advance of performance under the contract. Contract liabilities are recognized as revenue when we perform under the contract.


(In thousands)	September 30, 2019		December 31, 2018
Contract assets, included in other current assets	$	6	$	—
Contract liabilities - advance customer payments	$	427	$	366
Contract liabilities - deferred warranty revenue	$	235	$	218

Changes in contract assets in the nine months ended September 30, 2019 and the nine months ended September 30, 2018 resulted from unbilled amounts under sensor product arrangements and longer duration 3D scanning service projects in which revenue is recognized over time. Changes in contract liabilities primarily resulted from reclassification of beginning contract liabilities to revenue as performance obligations were satisfied or from cash received in advance and not recognized as revenue. See Note 8 for changes in contractual obligations related to deferred warranty revenue. Unsatisfied performance obligations are generally expected to be recognized as revenue over the next one to three years. There were no impairment losses for contract assets in the nine months ended September 30, 2019 or the nine months ended September 30, 2018.

The following summarizes the amounts reclassified from beginning contract liabilities to revenue:


	Three Months Ended September 30,				Nine Months Ended September 30,
(In thousands)	2019		2018			2019		2018
Amounts reclassified from beginning contract liabilities to revenue	$	342	$	39	$	401	$	262
Amounts reclassified from deferred warranty revenue		111		99	334		310
Total	$	453	$	138	$	735	$	572