Option Activity Under Plan (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share Based Compensation Plans [Line Items]
Weighted Average Remaining Contractual Term (In years), Outstanding	2 years 10 months 24 days
Employee Stock Option [Member]
Share Based Compensation Plans [Line Items]
Outstanding	5,752	5,428	6,032
Granted	1,315	349	325
Exercised	0	0	(525)
Forfeited/expired	0	(25)	(404)
Outstanding	7,067	5,752	5,428	6,032
Vested and expected to vest	6,728	5,666	5,428
Exercisable	5,442	5,079	4,735
Weighted - Average Exercise Price, Outstanding	$ 1.05	$ 1.03	$ 0.90
Weighted - Average Exercise Price, Granted	2.54	1.46	2.57
Weighted - Average Exercise Price, Exercised	0	0	0.83
Weighted - Average Exercise Price, Forfeited/expired	0	2.71	0.68
Weighted - Average Exercise Price, Outstanding	1.33	1.05	1.03	$ 0.90
Weighted - Average Exercise Price, Vested and expected to vest	1.27	1.04	1.03
Weighted - Average Exercise Price, Exercisable	$ 1.01	$ 1.00	$ 0.99
Weighted Average Remaining Contractual Term (In years), Outstanding	5 years 2 months 12 days	5 years 3 months 18 days	6 years	6 years 9 months 18 days
Weighted Average Remaining Contractual Term (In years), Granted	9 years 3 months 18 days	9 years 3 months 18 days	9 years 4 months 24 days
Weighted Average Remaining Contractual Term (In years), Vested and expected to vest	5 years	5 years 2 months 12 days	6 years
Weighted Average Remaining Contractual Term (In years), Exercisable	4 years 1 month 6 days	4 years 10 months 24 days	5 years 7 months 6 days
Aggregate Intrinsic Value, Outstanding	$ 1,972	$ 8,829	$ 18,672
Aggregate Intrinsic Value, Outstanding	2,241	1,972	8,829	$ 18,672
Aggregate Intrinsic Value, Vested and expected to vest	2,239	1,972	8,829
Aggregate Intrinsic Value, Exercisable	$ 2,236	$ 1,839	$ 7,931