Stock Incentive Plans - Summary of Expense Relating to Employee and Nonemployee Stock-Based Payment Awards from Stock Options and RSUs (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share based compensation, Total expensed	$ 367	$ 411	$ 812	$ 692
Cost of testing [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share based compensation, Total expensed	38	54	66	69
Research and Development Expense [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share based compensation, Total expensed	100	89	213	136
Sales and marketing [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share based compensation, Total expensed	43	36	71	56
General and administrative [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share based compensation, Total expensed	$ 186	$ 232	$ 462	$ 431