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 six months ended June 30, 2019 and the three and six months ended June 30, 2018:


	Three Months Ended June 30, 2019				Three Months Ended June 30, 2018
(In thousands except percentages)	Revenues		Percent of Revenues		Revenues		Percent of Revenues
Revenue recognized over time	$	292	2	%	$	1,127	7	%
Revenue recognized at a point in time		14,752	98	%		14,727	93	%
	$	15,044	100	%	$	15,854	100	%


	Six Months Ended June 30, 2019				Six Months Ended June 30, 2018
(In thousands except percentages)	Revenues		Percent of Revenues		Revenues		Percent of Revenues
Revenue recognized over time	$	638	2	%	$	2,021	7	%
Revenue recognized at a point in time		29,382	98	%		27,953	93	%
	$	30,020	100	%	$	29,974	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)	June 30, 2019		December 31, 2018
Contract assets, included in other current assets	$	6	$	—
Contract liabilities, included in advance customer payments/other liabilities	$	667	$	366

Changes in contract assets in the six months ended June 30, 2019 and the six months ended June 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 six months ended June 30, 2019 or the six months ended June 30, 2018.

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


	Three Months Ended June 30,				Six Months Ended June 30,
(In thousands)	2019		2018			2019		2018
Amounts reclassified from beginning contract liabilities to revenue	$	443	$	166	$	216	$	223
Amounts reclassified from deferred warranty revenue		110		91	224		211
Total	$	553	$	257	$	440	$	434