Revenue

Disaggregation of revenue

The following table shows net sales classified by major product category for the three months ended March 31, 2019 and 2018:



	Three Months Ended March 31,
(in thousands)	2019		2018
Structural components	$	141,276	$	135,829
Lumber & lumber sheet goods	241,959		288,086
Millwork, doors & windows	239,922		229,518
Other building products & services	202,248		180,769
Total net sales	$	825,405	$	834,202

The following table reflects the Company’s estimate of net sales by each customer type for the three months ended March 31, 2019 and 2018. Certain previously reported amounts for the three months ended March 31, 2018 were revised in the table below. The revisions were not material to the previously issued financial statements.



	Three Months Ended March 31,
(in thousands)	2019		2018
Single-family homebuilders	$	628,718	$	638,858
Remodeling contractors	88,208		96,146
Multi-family, commercial & other contractors	108,479		99,198
Total net sales	$	825,405	$	834,202

Contract balances

The following table reflects the Company’s contract balances as of March 31, 2019 and December 31, 2018:



(in thousands)	March 31, 2019		December 31, 2018		Change
Receivables, including unbilled receivables presented in prepaid expenses and other current assets	$	329,788	$	306,370	$	23,418
Contract assets	33,778		32,348		1,430
Contract liabilities	$	32,961	$	34,888	$	(1,927	)

During the three months ended March 31, 2019, the Company’s contract assets increased by $1.4 million and the Company’s contract liabilities decreased by $1.9 million. The change in contract assets and liabilities was primarily due to the timing of revenue recognition, as the balances were not materially impacted by any other factors. For the three months ended March 31, 2019, the Company recognized revenue of $27.7 million that was included in contract liabilities as of December 31, 2018. Revenue recognized related to performance obligations that were satisfied or partially satisfied in previous periods was not material for the three months ended March 31, 2019.

As permitted by Topic 606, the Company has elected not to disclose the value of unsatisfied performance obligations, as the Company’s contracts generally have an original expected length of one year or less.