Segment Reporting (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Product revenues	$ 258,939	$ 235,853	$ 784,607	$ 728,498
Type of Revenue [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember
Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	100.00%	100.00%	100.00%	100.00%
United States
Segment Reporting Information [Line Items]
Product revenues	$ 125,936	$ 104,033	$ 369,798	$ 337,697
United States | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	49.00%	44.00%	47.00%	46.00%
China
Segment Reporting Information [Line Items]
Product revenues	$ 22,756	$ 25,741	$ 71,887	$ 66,168
China | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	9.00%	11.00%	9.00%	9.00%
Germany
Segment Reporting Information [Line Items]
Product revenues	$ 22,681	$ 17,711	$ 68,670	$ 53,273
Germany | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	9.00%	7.00%	9.00%	7.00%
South Korea
Segment Reporting Information [Line Items]
Product revenues	$ 12,814	$ 16,569	$ 42,419	$ 50,714
South Korea | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	5.00%	7.00%	5.00%	7.00%
Japan
Segment Reporting Information [Line Items]
Product revenues	$ 16,672	$ 15,727	$ 43,520	$ 43,103
Japan | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	6.00%	7.00%	6.00%	6.00%
Canada
Segment Reporting Information [Line Items]
Product revenues	$ 7,778	$ 10,667	$ 33,482	$ 32,709
Canada | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	3.00%	5.00%	4.00%	5.00%
Czech Republic
Segment Reporting Information [Line Items]
Product revenues	$ 10,742	$ 9,175	$ 33,563	$ 29,826
Czech Republic | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	4.00%	4.00%	4.00%	4.00%
United Kingdom
Segment Reporting Information [Line Items]
Product revenues	$ 9,037	$ 8,143	$ 28,349	$ 26,250
United Kingdom | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	3.00%	3.00%	4.00%	4.00%
Romania
Segment Reporting Information [Line Items]
Product revenues	$ 5,876	$ 5,091	$ 16,775	$ 13,173
Romania | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	2.00%	2.00%	2.00%	2.00%
Other
Segment Reporting Information [Line Items]
Product revenues	$ 24,647	$ 22,996	$ 76,144	$ 75,585
Other | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	10.00%	10.00%	10.00%	10.00%
Non U.S.
Segment Reporting Information [Line Items]
Product revenues	$ 133,003	$ 131,820	$ 414,809	$ 390,801
Non U.S. | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	51.00%	56.00%	53.00%	54.00%