Stockholders' Equity - Changes in Accumulated Other Comprehensive Income (Loss) (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 115
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Other comprehensive income before reclassifications	0
Amounts reclassified from accumulated other comprehensive income (loss)	(16)
Net current period other comprehensive income (loss)	(16)
Ending Balance	99
Unrealized Gains and Losses on Available-for Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(7)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Other comprehensive income before reclassifications	0
Amounts reclassified from accumulated other comprehensive income (loss)	(16)
Net current period other comprehensive income (loss)	(16)
Ending Balance	(23)
Foreign Currency Items
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	122
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Other comprehensive income before reclassifications	0
Amounts reclassified from accumulated other comprehensive income (loss)
Net current period other comprehensive income (loss)	0
Ending Balance	$ 122