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, 2017	Dec. 31, 2016	Dec. 31, 2015
Customer A
Revenue, Major Customer [Line Items]
Concentration risk percentage	21.30%	20.10%	19.40%
Customer A | AIT
Revenue, Major Customer [Line Items]
Concentration risk percentage	6.30%	5.90%	5.50%
Customer A | EVM
Revenue, Major Customer [Line Items]
Concentration risk percentage	15.00%	14.20%	13.90%
Customer B
Revenue, Major Customer [Line Items]
Concentration risk percentage	14.20%	13.20%	12.70%
Customer B | AIT
Revenue, Major Customer [Line Items]
Concentration risk percentage	5.30%	5.00%	4.60%
Customer B | EVM
Revenue, Major Customer [Line Items]
Concentration risk percentage	8.90%	8.20%	8.10%
Customer C
Revenue, Major Customer [Line Items]
Concentration risk percentage	13.20%	12.40%	11.60%
Customer C | AIT
Revenue, Major Customer [Line Items]
Concentration risk percentage	6.20%	5.30%	5.20%
Customer C | EVM
Revenue, Major Customer [Line Items]
Concentration risk percentage	7.00%	7.10%	6.40%