Components of Expense Relating to ESPP (Detail) (Employee Stock Purchase Plan, USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Allocated share based compensation expense	$ 278	$ 320
Cost of Goods Sold
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Allocated share based compensation expense	80	67
Research and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Allocated share based compensation expense	120	176
Selling and Marketing Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Allocated share based compensation expense	38	40
General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Allocated share based compensation expense	$ 40	$ 37