Income Taxes - Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Beginning balance	$ 43	$ 311	$ 232
Increases based on tax positions related to prior years	109
Decreases based on tax positions related to prior years		(79)
Decreases due to ownership change		(232)
Increases based on tax positions in current year	112	43	79
Settlement	0	0	0
Lapse of statute of limitations	0	0	0
Ending balance	$ 264	$ 43	$ 311