3. REVENUE

Revenue is recognized when obligations under the terms of a contract (purchase orders) with our customers are satisfied; generally, this occurs with the transfer of control of our products. Revenue is measured as the amount of consideration we expect to receive in exchange for transferring goods. Shipping cost incurred by us to deliver products to our customers are recorded in cost of sales. The expected costs associated with our warranties continue to be recognized as expense when the products are sold. We recognize revenue as of a point in time.

During 2018, 2017 and 2016, LP's top ten customers accounted for approximately 44%, 46% and 41% of its sales in the aggregate. No individual customer exceeded 10% of LP's sales in 2018, 2017 or 2016.

Customer programs and incentives are a common practice in our businesses. Our businesses incur customer program costs to obtain favorable product placement, to promote sales of products and to maintain competitive pricing. Customer program costs and incentives, including rebates and promotion and volume allowances, are accounted for as deductions from net sales at the time the program is initiated. These reductions from revenue are recorded at the later of the time of sale or the implementation of the program based on management’s best estimates. Estimates are based on historical and projected experience for each type of program or customer. Volume allowances are accrued based on management’s estimates of customer volume achievement and other factors incorporated into customer agreements, such as new product purchases, store sell-through and merchandising support. Management periodically reviews accruals for these rebates and allowances, and adjusts accruals when circumstances indicate (typically as a result of a change in volume expectations). As of December 31, 2018 and 2017; we had $30.1 million and $24.2 million accrued as customer rebates recorded in Accounts payable and accrued liabilities on our Consolidated Balance Sheets.

We ship some of our products to customers' distribution centers on a consignment basis. We retain title to our products stored at the distribution centers. As our products are removed from the distribution centers by retailers and shipped to retailers’ stores, title passes from us to the retailers. At that time, we invoice the retailers and recognize revenue for these consignment transactions. We do not offer a right of return for products shipped to the retailers’ stores from the distribution centers. The amount of consignment inventory as of December 31, 2018 and 2017 was $9.5 million and $18.3 million.

The following tables disaggregate our revenue by product line and product type by segment for the years ended December 31:



Year Ended December 31, 2018
By Product family:	Siding		OSB		EWP		South America		Other		Inter-segment			Total
SmartSide^® Strand siding	$	724.8	$	—	$	—	$	21.5	$	—	$	—		$	746.3
SmartSide^® Fiber siding	106.4		—		—		—		—		—			106.4
CanExel^® siding	37.3		—		—		—		—		—			37.3
OSB - commodity	39.4		746.0		9.9		—		—		(0.1		)	795.2
OSB - value-add	22.5		550.9		13.9		135.2		—		—			722.5
LVL	—		—		140.9		—		—		—			140.9
LSL	—		—		59.2		—		—		—			59.2
I-joist	—		—		122.1		—		—		—			122.1
Plywood	—		—		28.7		—		—		—			28.7
Other	11.9		8.3		16.2		4.1		28.9		—			69.4
	$	942.3	$	1,305.2	$	390.9	$	160.8	$	28.9	$	(0.1	)	$	2,828.0
By Product type:
Commodity	$	39.4	$	746.0	$	38.6	$	—	$	—	$	(0.1	)	$	823.9
Value-add	891.0		550.9		336.1		156.7		—		—			1,934.7
Other	11.9		8.3		16.2		4.1		28.9		—			69.4
	$	942.3	$	1,305.2	$	390.9	$	160.8	$	28.9	$	(0.1	)	$	2,828.0



Year Ended December 31, 2017
By Product family:	Siding		OSB		EWP		South America		Other		Inter-segment			Total
SmartSide^® Strand siding	$	646.3	$	—	$	—	$	19.7	$	—	$	(3.6	)	$	662.4
SmartSide^® Fiber siding	111.3		—		—		—		—		—			111.3
CanExel^® siding	49.4		—		—		—		—		—			49.4
OSB - commodity	66.9		765.5		9.4		—		—		—			841.8
OSB - value-add	—		524.7		13.2		131.7		—		—			669.6
LVL	—		—		144.3		—		—		—			144.3
LSL	—		—		46.8		—		—		(0.1		)	46.7
I-joist	—		—		116.9		—		—		(0.1		)	116.8
Plywood	—		—		25.1		—		—		—			25.1
Other	10.1		12.3		10.2		3.9		30.0		—			66.5
	$	884.0	$	1,302.5	$	365.9	$	155.3	$	30.0	$	(3.8	)	$	2,733.9
By Product type:
Commodity	$	66.9	$	765.5	$	34.5	$	—	$	—	$	—		$	866.9
Value-add	807.0		524.7		321.2		151.4		—		(3.8		)	1,800.5
Other	10.1		12.3		10.2		3.9		30.0		—			66.5
	$	884.0	$	1,302.5	$	365.9	$	155.3	$	30.0	$	(3.8	)	$	2,733.9



Year Ended December 31, 2016
By Product family:	Siding		OSB		EWP		South America		Other		Inter-segment			Total
SmartSide^® Strand siding	$	549.5	$	—	$	—	$	19.6	$	—	$	(1.5	)	$	567.6
SmartSide^® Fiber siding	108.1		—		—		—		—		—			108.1
CanExel^® siding	43.2		—		—		—		—		—			43.2
OSB - commodity	40.8		626.0		0.1		—		—		(5.8		)	661.1
OSB - value-add	1.8		390.3		10.7		112.3		—		—			515.1
LVL	—		—		122.1		—		—		—			122.1
LSL	—		—		37.8		—		—		—			37.8
I-joist	—		—		99.4		—		—		—			99.4
Plywood	—		—		15.8		—		—		—			15.8
Other	8.9		11.4		11.0		5.0		26.9		—			63.2
	$	752.3	$	1,027.7	$	296.9	$	136.9	$	26.9	$	(7.3	)	$	2,233.4
By Product type:
Commodity	$	40.8	$	626.0	$	15.9	$	—	$	—	$	(5.8	)	$	676.9
Value-add	702.6		390.3		270.0		131.9		—		(1.5		)	1,493.3
Other	8.9		11.4		11.0		5.0		26.9		—			63.2
	$	752.3	$	1,027.7	$	296.9	$	136.9	$	26.9	$	(7.3	)	$	2,233.4