Segment Information - Summary of Revenues on Percentage Basis by Geographic Region (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Revenues on a percentage basis by geographic region, based on the country	100.00%	100.00%	100.00%	100.00%
United States [Member]
Segment Reporting Information [Line Items]
Revenues on a percentage basis by geographic region, based on the country	58.00%	71.00%	64.00%	68.00%
South America [Member]
Segment Reporting Information [Line Items]
Revenues on a percentage basis by geographic region, based on the country	9.00%	8.00%	10.00%	9.00%
Japan [Member]
Segment Reporting Information [Line Items]
Revenues on a percentage basis by geographic region, based on the country	7.00%	2.00%	4.00%	2.00%
Europe [Member]
Segment Reporting Information [Line Items]
Revenues on a percentage basis by geographic region, based on the country	18.00%	14.00%	15.00%	15.00%
Other [Member]
Segment Reporting Information [Line Items]
Revenues on a percentage basis by geographic region, based on the country	8.00%	5.00%	7.00%	6.00%