Revenue (Tables)

12 Months Ended

Dec. 31, 2019

Revenue from Contract with Customer [Abstract]

Schedule of Sales by Major Source

The following table reflects our sales disaggregated by major source for the year ended December 31, 2019 (in thousands):

	Year Ended December 31, 2019						Year Ended December 31, 2018
Category	Oil & Gas Proppants		Industrial & Specialty Products		Total Sales		Oil & Gas Proppants		Industrial & Specialty Products		Total Sales
Product	$	704,516	$	463,956	$	1,168,472	$	888,509	$	394,290	$	1,282,799
Service	306,005		—		306,005		294,482		17		294,499
Total Sales	$	1,010,521	$	463,956	$	1,474,477	$	1,182,991	$	394,307	$	1,577,298

Schedule of Changes in Contract Assets and Liabilities

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 year ended December 31, 2019 (in thousands):

	Unbilled Receivables
	December 31, 2019			December 31, 2018
Beginning Balance	$	90		$	5,245
Reclassifications to billed receivables	(3,983		)	(11,157		)
Revenues recognized in excess of period billings	4,037			6,002
Ending Balance	$	144		$	90

	Deferred Revenue
	December 31, 2019			December 31, 2018
Beginning Balance	$	113,319		$	118,414
Revenues recognized from balances held at the beginning of the period	(65,225		)	(33,381		)
Revenues deferred from period collections on unfulfilled performance obligations	12,225			31,625
Revenues recognized from period collections	(9,685		)	(3,339		)
Ending Balance	$	50,634		$	113,319