Summary of Stock Option and Restricted Stock Activity (Detail) - $ / shares	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of shares, Beginning Balance	5,713
Options granted, Shares	446
Options forfeited, Shares	(245)
Options expired, Shares	(485)
Options exercised, Shares	(18)
Number of shares, Ending Balance	5,411	5,713
Weighted average exercise price, Beginning Balance	$ 5.33
Options granted, Weighted average exercise price	2.82
Options forfeited, Weighted average exercise price	3.26
Options expired, Weighted average exercise price	6.16
Options exercised, Weighted average exercise price	2.69
Weighted average exercise price, Ending Balance	$ 5.15	$ 5.33
Weighted average remaining contractual term, End of the period	5 years 8 months 1 day	5 years 11 months 4 days