Deferred Revenue

6 Months Ended

Jun. 30, 2018

Deferred Revenue Disclosure [Abstract]

DEFERRED REVENUE

NOTE J—DEFERRED REVENUE

We enter into certain customer supply agreements which give the customers the right to purchase certain products for a discounted price at certain volumes over an average initial contract term of one to five years. The advance payments represent future purchases and are recorded as deferred revenue, recognized as revenue over the contract term of each supply agreement. During the six months ended June 30, 2018 we received advances of $13.4 million. At June 30, 2018 and December 31, 2017, the total deferred revenue balance was $111.4 million and $118.4 million, respectively, of which $52.0 million and $36.1 million was classified as current on our Balance Sheets.

NOTE S— REVENUE

We consider sales disaggregated at the product and service level by segment to depict how the nature, amount, timing and uncertainty of revenues and cash flow are impacted by changes in economic factors. The following table disaggregates our sales by major source for the three and six months ended June 30, 2018 (in thousands):

	Three Months Ended   June 30, 2018						Six Months Ended   June 30, 2018
Category	Oil & Gas Proppants		Industrial & Specialty Products		Total Sales		Oil & Gas Proppants		Industrial & Specialty Products		Total Sales
Product	$	242,587	$	103,370	$	345,957	$	481,009	$	159,736	$	640,745
Service	81,476		—		81,476		155,984		17		156,001
Total Sales	$	324,063	$	103,370	$	427,433	$	636,993	$	159,753	$	796,746

The following tables reflect the changes in our contract assets, which we classify as unbilled receivables and our contract liabilities, which we classify as deferred revenues, for the six months ended June 30, 2018 (in thousands):

	Unbilled Receivables
December 31, 2017	$	5,245
Reclassifications to billed receivables	(8,161		)
Revenues recognized in excess of period billings	5,428
June 30, 2018	$	2,512

	Deferred Revenue
December 31, 2017	$	118,414
Revenues recognized from balances held at the beginning of the period	(20,344		)
Revenues deferred from period collections on unfulfilled performance obligations	13,375
June 30, 2018	$	111,445

We have elected to use the practical expedients allowed under ASC 606-10-50-14, pursuant to which we have excluded disclosures of transaction prices allocated to remaining performance obligations and when we expect to recognize such revenue. The majority of our remaining performance obligations are primarily comprised of unfulfilled product, transportation service, and labor service orders, all of which hold a remaining duration of less than one year. The long term portion of deferred revenue primarily represents a combination of refundable and nonrefundable customer prepayments for which related current performance obligations do not yet exist, but are expected to arise, before the expiration of the contract. Our residual unfulfilled performance obligations are comprised primarily of long-term equipment rental arrangements in which we recognize revenues equal to what we have a right to invoice. Generally, no variable consideration exists related to our remaining performance obligations and no consideration is excluded from the associated transaction prices.