Other Income (Expense), Net - Components of Other Income (Expense), Net (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Other Income and Expenses [Abstract]
Interest income	$ 179	$ 118	$ 380	$ 235
Other income (expense)	(230)	(5)	(209)	(8)
Fair value adjustment to derivative liability	0	225	0	225
Total other income (expense), net	$ (51)	$ 338	$ 171	$ 452