Revenue

3 Months Ended

Mar. 31, 2020

Revenue from Contract with Customer [Abstract]

REVENUE

NOTE S— REVENUE

We consider sales disaggregated at the product and service level by business 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 months ended March 31, 2020 and 2019 (in thousands):

	Three Months Ended   March 31, 2020						Three Months Ended   March 31, 2019
Category	Oil & Gas Proppants		Industrial & Specialty Products		Total Sales		Oil & Gas Proppants		Industrial & Specialty Products		Total Sales
Product	$	108,277	$	113,884	$	222,161	$	178,587	$	118,273	$	296,860
Service	47,438		—		47,438		81,890		—		81,890
Total Sales	$	155,715	$	113,884	$	269,599	$	260,477	$	118,273	$	378,750

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 three months ended March 31, 2020 and 2019 (in thousands):

	Unbilled Receivables
	March 31, 2020			March 31, 2019
Beginning Balance	$	144		$	90
Reclassifications to billed receivables	(144		)	(90		)
Revenues recognized in excess of period billings	108			1,641
Ending Balance	$	108		$	1,641

	Deferred Revenue
	March 31, 2020			March 31, 2019
Beginning Balance	$	50,634		$	113,319
Revenues recognized from balances held at the beginning of the period	(2,525		)	(6,704		)
Revenues deferred from period collections on unfulfilled performance obligations	—			10,025
Revenues recognized from period collections	—			(872		)
Ending Balance	$	48,109		$	115,768

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.

Foreign Operations

The following table includes information related to our foreign operations for the three months ended March 31, 2020 and 2019:

	March 31, 2020		March 31, 2019
Total Sales	$	21,605	$	15,300
Pre-tax income	$	4,213	$	900
Net income	$	3,328	$	800
Consolidated Assets	$	29,705	$	10,100