Income Taxes - Summary of Changes in Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Balance at the beginning of the year	$ 236	$ 315	$ 52
Gross increases for tax positions taken in the current year	0	0	0
Gross increases for tax positions taken in prior years	0	0	283
Gross decreases in tax positions due to lapse in statute of limitations	(119)	(79)	(20)
Gross decreases for tax positions taken in prior years	0	0	0
Gross decreases for tax settlements with taxing authorities	0	0	0
Balance at the end of the year	$ 117	$ 236	$ 315