Income Taxes - Schedule of Net Loss by Jurisdiction (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Net loss, Total	$ 29,497	$ 42,854
Domestic [Member]
Income Taxes [Line Items]
Net loss, Total	28,281	41,821
Foreign [Member]
Income Taxes [Line Items]
Net loss, Total	$ 1,216	$ 1,033