Cash Proceeds Along with Fair Value Disclosures Related to Grants, Exercises, and Vesting Options (Detail) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Proceeds from stock options exercised		$ 3	$ 1	$ 44
Intrinsic value of stock options exercised	[1]	$ 1		$ 52
Weighted-average fair value of options granted		$ 0.69	$ 1.03	$ 1.54
Total fair value of shares vested during the year		$ 1,286	$ 1,728	$ 2,268

[1] The intrinsic value of stock options exercised is the amount by which the market price of the stock on the date of exercise exceeded the market price of the stock on the date of grant.