Industry and Geographic Information - Sales to Individual Customers in Excess of 10% of Total Revenue (Detail) - Sales [Member]	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Major Customer [Line Items]
Sales percentage	10.00%
Customer Concentration Risk [Member]
Revenue, Major Customer [Line Items]
Sales percentage	44.00%	54.00%	44.00%
Customer Concentration Risk [Member] | Customer A [Member]
Revenue, Major Customer [Line Items]
Sales percentage	19.00%	20.00%	15.00%
Customer Concentration Risk [Member] | Customer B [Member]
Revenue, Major Customer [Line Items]
Sales percentage	13.00%	13.00%	13.00%
Customer Concentration Risk [Member] | Customer C [Member]
Revenue, Major Customer [Line Items]
Sales percentage	12.00%	21.00%	16.00%