Segment Information and Geographic Data - Net Sales to Significant Customers as a Percent of Total Net Sales (Detail) - Sales Revenue, Net - Customer Concentration Risk	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Customer A
Revenue, Major Customer [Line Items]
Concentration risk percentage	20.30%	21.30%	20.10%
Customer A | AIT
Revenue, Major Customer [Line Items]
Concentration risk percentage	6.20%	6.30%	5.90%
Customer A | EVM
Revenue, Major Customer [Line Items]
Concentration risk percentage	14.10%	15.00%	14.20%
Customer B
Revenue, Major Customer [Line Items]
Concentration risk percentage	15.70%	14.20%	13.20%
Customer B | AIT
Revenue, Major Customer [Line Items]
Concentration risk percentage	5.60%	5.30%	5.00%
Customer B | EVM
Revenue, Major Customer [Line Items]
Concentration risk percentage	10.10%	8.90%	8.20%
Customer C
Revenue, Major Customer [Line Items]
Concentration risk percentage	14.10%	13.20%	12.40%
Customer C | AIT
Revenue, Major Customer [Line Items]
Concentration risk percentage	6.20%	6.20%	5.30%
Customer C | EVM
Revenue, Major Customer [Line Items]
Concentration risk percentage	7.90%	7.00%	7.10%