Property, Plant and Equipment - Schedule of Property, Plant and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Cost	$ 184,109	$ 173,867
Accumulated depreciation	(138,970)	(124,951)
Property, plant and equipment, net	45,139	48,916
Buildings [Member]
Property Plant And Equipment [Line Items]
Cost	3,725	3,225
Plant and equipment [Member]
Property Plant And Equipment [Line Items]
Cost	47,588	43,745
Instrumentation [Member]
Property Plant And Equipment [Line Items]
Cost	75,818	71,962
Furniture and fixtures [Member]
Property Plant And Equipment [Line Items]
Cost	7,605	8,308
Computer software [Member]
Property Plant And Equipment [Line Items]
Cost	48,604	44,720
Construction in progress [Member]
Property Plant And Equipment [Line Items]
Cost	$ 769	$ 1,907