Summary of Activity under Stock-Based Compensation Plans (Detail)	9 Months Ended
	Sep. 30, 2016 $ / shares shares
Stock Options Number Outstanding
Beginning Balance | shares	781,804
Granted | shares	444,460
Cancelled or Expired | shares	(299,929)
Ending Balance | shares	926,335
Vested or expected to vest at September 30, 2016 | shares	887,433
Exercisable at September 30, 2016 | shares	458,897
Stock Options Average Exercise Price per share
Beginning Balance | $ / shares	$ 11.48
Granted | $ / shares	4.36
Cancelled or Expired | $ / shares	12.81
Ending Balance | $ / shares	7.40
Vested or expected to vest at September 30, 2016 | $ / shares	7.49
Exercisable at September 30, 2016 | $ / shares	$ 9.12
Stock Options Remaining Contractual Life (in years)
Remaining Contractual Life	8 years 1 month 24 days
Vested or expected to vest at September 30, 2016	8 years 1 month 6 days
Exercisable at September 30, 2016	7 years 2 months 16 days