Segment Reporting (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Product revenues	$ 261,889	$ 249,267
Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	100.00%	100.00%
United States
Segment Reporting Information [Line Items]
Product revenues	$ 120,350	$ 119,523
United States | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	46.00%	48.00%
China
Segment Reporting Information [Line Items]
Product revenues	$ 24,204	$ 20,465
China | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	9.00%	8.00%
Germany
Segment Reporting Information [Line Items]
Product revenues	$ 22,362	$ 17,868
Germany | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	9.00%	7.00%
South Korea
Segment Reporting Information [Line Items]
Product revenues	$ 13,822	$ 16,391
South Korea | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	5.00%	7.00%
Japan
Segment Reporting Information [Line Items]
Product revenues	$ 13,573	$ 14,283
Japan | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	5.00%	6.00%
Canada
Segment Reporting Information [Line Items]
Product revenues	$ 13,113	$ 10,929
Canada | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	5.00%	4.00%
Czech Republic
Segment Reporting Information [Line Items]
Product revenues	$ 11,715	$ 10,707
Czech Republic | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	4.00%	4.00%
United Kingdom
Segment Reporting Information [Line Items]
Product revenues	$ 10,845	$ 9,668
United Kingdom | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	4.00%	4.00%
Mexico
Segment Reporting Information [Line Items]
Product revenues	$ 6,298	$ 5,370
Mexico | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	3.00%	2.00%
Other
Segment Reporting Information [Line Items]
Product revenues	$ 25,607	$ 24,063
Other | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	10.00%	10.00%
Non U.S.
Segment Reporting Information [Line Items]
Product revenues	$ 141,539	$ 129,744
Non U.S. | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	54.00%	52.00%