Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Tax Disclosure [Abstract]
Income tax provision	$ 96	$ 343	$ 182	$ 622
Effective income tax rate	(0.30%)	(1.60%)	(0.30%)	(1.40%)