Stock Option Activity (Detail)	3 Months Ended
	Mar. 31, 2016 USD ($) $ / shares shares
Options
Outstanding at beginning of period | shares	4,796,005
Granted | shares	1,139,500
Forfeited | shares	(351,085)
Outstanding at end of period | shares	5,584,420
Vested or expected to vest at March 31, 2016 | shares	3,176,655
Exercisable at March 31, 2016 | shares	2,537,373
Weighted-Average Exercise Price
Outstanding at beginning of period | $ / shares	$ 3.78
Granted | $ / shares	1.08
Forfeited | $ / shares	1.38
Outstanding at end of period | $ / shares	3.38
Vested or expected to vest at March 31, 2016 | $ / shares	5.04
Exercisable at March 31, 2016 | $ / shares	$ 6.00
Weighted-Average Remaining Contractual Term
Outstanding at March 31, 2016	7 years 2 months 1 day
Vested or expected to vest at March 31, 2016	5 years 9 months 26 days
Exercisable at March 31, 2016	4 years 11 months 27 days
Aggregate Intrinsic Value
Outstanding at end of year | $	$ 88,258
Vested or expected to vest at end of year | $	43,329
Exercisable at end of year | $	$ 27,625