on the relationship of costs incurred to date to total anticipated costs (the cost-to-cost approach). Under the cost-to-cost approach, the use of estimated costs to complete each contract is a significant variable in the process of determining recognized revenue, requires judgment and can change throughout the duration of a contract due to contract modifications and other factors impacting job completion. The costs of earned revenue include all direct material and labor costs and those indirect costs related to contract performance, such as indirect labor, supplies, tools and repairs. Provisions for estimated losses on uncompleted contracts are made in the period in which such losses are determined.

Our long-term contracts can be subject to modification to account for changes in contract specifications and requirements. We consider contract modifications to exist when the modification either creates new, or changes the existing, enforceable rights and obligations. Most of our contract modifications are for goods or services that are not distinct from the existing contract due to the significant integration service provided in the context of the contract and are accounted for as if they were part of that existing contract. The effect of a contract modification on the transaction price and our measure of progress for the performance obligation to which it relates, is recognized as an adjustment to revenue (either as an increase in or a reduction of revenue) on a cumulative

catch-up

basis.

Sales terms typically do not exceed 30 days for short-term contracts and typically do not exceed 60 days for long-term contracts with customers. All contracts are billed either contractually or as work is performed. Billing on our long-term contracts occurs primarily on a monthly basis throughout the contract period whereby we submit invoices for customer payment based on actual or estimated costs incurred during the billing period. On certain of our long-term contracts the customer may withhold payment on an invoice equal to a percentage of the invoice amount, which will be subsequently paid after satisfactory completion of each installation project. This amount is referred to as retainage and is common practice in the construction industry, as it allows for customers to ensure the quality of the service performed prior to full payment. Retainage receivables are classified as current or long-term assets based on the expected time to project completion.

We disaggregate our revenue from contracts with customers by end market and product, as we believe it best depicts how the nature, amount, timing and uncertainty of our revenue and cash flows are affected by economic factors. The following tables present our revenues disaggregated by end market and product (in thousands):


	Three months ended June 30,								Six months ended June 30,
	2019				2018				2019				2018
Residential new construction	$	282,494	76	%	$	257,904	77	%	$	543,804	76	%	$	487,546	77	%
Repair and remodel		24,705	7	%		21,873	7	%		46,225	7	%		42,345	7	%
Commercial		64,615	17	%		52,807	16	%		123,920	17	%		104,421	16	%

Net revenues	$	371,814	100	%	$	332,584	100	%	$	713,949	100	%	$	634,312	100	%


	Three months ended June 30,								Six months ended June 30,
	2019				2018				2019				2018
Insulation	$	235,473	63	%	$	218,493	66	%	$	456,695	64	%	$	420,768	67	%
Waterproofing		28,858	8	%		24,892	7	%		51,243	7	%		47,498	7	%
Shower doors, shelving and mirrors		26,900	7	%		22,773	7	%		50,817	7	%		43,032	7	%
Garage doors		21,782	6	%		19,326	6	%		43,454	6	%		34,792	5	%
Rain gutters		12,996	4	%		10,608	3	%		24,195	3	%		19,266	3	%
Window blinds		10,781	3	%		8,079	2	%		20,165	3	%		13,385	2	%
Other building products		35,024	9	%		28,413	9	%		67,380	10	%		55,571	9	%

Net revenues	$	371,814	100	%	$	332,584	100	%	$	713,949	100	%	$	634,312	100	%

Contract Assets and Liabilities

Our contract assets consist of unbilled amounts typically resulting from sales under contracts when the

cost-to-cost

method of revenue recognition is utilized and revenue recognized, based on costs incurred, exceeds the amount billed to the customer. Our contract assets are recorded in other current assets in our Condensed Consolidated Balance Sheets. Our contract liabilities consist of customer deposits and billings in excess of revenue recognized, based on costs incurred and is included in other current liabilities in our Consolidated Balance Sheets.

Contract assets and liabilities related to our uncompleted contracts and customer deposits were as follows (in thousands):


	June 30,			December 31,
	2019			2018
Contract assets	$	20,207		$	15,092
Contract liabilities		(7,380	)		(7,468	)

Uncompleted contracts were as follows (in thousands):


	June 30,		December 31,
	2019		2018
Costs incurred on uncompleted contracts	$	99,087	$	114,826
Estimated earnings		53,596		58,952

Total		152,683		173,778
Less: Billings to date		136,857		163,112

Net under (over) billings	$	15,826	$	10,666

Net under (over) billings were as follows (in thousands):


	June 30,			December 31,
	2019			2018
Costs and estimated earnings in excess of billings on uncompleted contracts (contract assets)	$	20,207		$	15,092
Billings in excess of costs and estimated earnings on uncompleted contracts (contract liabilities)		(4,381	)		(4,426	)

Net under (over) billings	$	15,826		$	10,666

The difference between contract assets and contract liabilities as of June 30, 2019 compared to December 31, 2018 is primarily the result of timing differences between our performance of obligations under contracts and customer payments. During the three and six months ended June 30, 2019, we recognized $0.8 million and $7.1 million of revenue that was included in the contract liability balance at December 31, 2018. We did not recognize any impairment losses on our receivables and contract assets during the three and six months ended June 30, 2019 or 2018.

Remaining performance obligations represent the transaction price of contracts for which work has not been performed and excludes unexercised contract options and potential modifications. As of June 30, 2019, the aggregate amount of the transaction price allocated to remaining uncompleted contracts was $87.4 million. We expect to satisfy remaining performance obligations and recognize revenue on substantially all of these uncompleted contracts

over the next 18 months.

Practical Expedients and Exemptions

We generally expense sales commissions and other incremental costs of obtaining a contract when incurred because the amortization period is usually one year or less. Sales commissions are recorded within selling expenses on the Condensed Consolidated Statements of Operations and Comprehensive Income.

We do not disclose the value of unsatisfied performance obligations for contracts with an original expected length of

one year or less.