Significant Accounting Policies - Narrative (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Line Items]
Percentage of foreign and export sales	54.20%	46.90%	44.20%
Export sales	$ 55,900	$ 53,200	$ 52,500
Percentage of sales to automotive market	48.30%	56.20%	56.60%
Progress billings adjustment	$ 1,661	$ 893
Finite-lived intangible asset useful life	11 years
Research and development expense	$ 10,800	$ 9,000	$ 8,500
Minimum
Accounting Policies [Line Items]
Finite-lived intangible asset useful life	4 years
Maximum
Accounting Policies [Line Items]
Finite-lived intangible asset useful life	14 years
Ford Motor Company
Accounting Policies [Line Items]
Percentage of accounts receivable from significant customer	12.00%	14.20%