Summary of Option Activity (Detail) - 2002 Stock Incentive Plan - $ / shares shares in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Shares
Beginning Balance	6,737
Granted at fair market value	2,519
Exercised	(6)
Forfeited, cancelled, or expired	(471)
Ending Balance	8,779	6,737
Options exercisable at March 31, 2018	4,264
Vested options expired during the quarter ended March 31, 2018	920
Weighted Average Exercise Price
Beginning Balance	$ 1.80
Granted at fair market value	0.42
Exercised	0.42
Forfeited, cancelled, or expired	3.58
Ending Balance	1.40	$ 1.80
Options exercisable at March 31, 2018	1.88
Vested options expired during the quarter ended March 31, 2018	$ 2.79
Weighted Average Remaining Contractual Term (Years)
Options outstanding	7 years 5 months 4 days	7 years 2 months 15 days
Options exercisable	5 years 7 months 13 days