Industry and Geographic Information - Sales to Individual Customers in Excess of 10% of Total Revenues (Detail) - Sales [Member]	3 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2017
Revenue, Major Customer [Line Items]
Sales percentage		10.00%
Customer Concentration Risk [Member]
Revenue, Major Customer [Line Items]
Sales percentage	43.00%	55.00%
Customer Concentration Risk [Member] | Customer A [Member]
Revenue, Major Customer [Line Items]
Sales percentage	16.00%	21.00%
Customer Concentration Risk [Member] | Customer B [Member]
Revenue, Major Customer [Line Items]
Sales percentage	14.00%	21.00%
Customer Concentration Risk [Member] | Customer C [Member]
Revenue, Major Customer [Line Items]
Sales percentage	13.00%	13.00%