Summary of Activity under Stock-Based Compensation Plans (Detail) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($) $ / shares shares
Stock Options Number Outstanding
Beginning Balance | shares	832,941
Cancelled or Expired | shares	(142,629)
Ending Balance | shares	690,312
Vested or expected to vest at June 30, 2017 | shares	671,191
Exercisable at June 30, 2017 | shares	410,132
Stock Options Average Exercise Price per share
Beginning Balance | $ / shares	$ 7.11
Cancelled or Expired | $ / shares	10.50
Ending Balance | $ / shares	6.41
Vested or expected to vest at June 30, 2017 | $ / shares	6.46
Exercisable at June 30, 2017 | $ / shares	$ 7.44
Stock Options Remaining Contractual Life (in years)
Remaining Contractual Life	7 years 10 months 6 days
Vested or expected to vest at June 30, 2017	7 years 9 months 29 days
Exercisable at June 30, 2017	7 years 3 months 8 days
Stock Options Average Intrinsic Value
Average intrinsic value | $	$ 396,594
Vested or expected to vest at June 30, 2017 | $	380,325
Exercisable at June 30, 2017 | $	$ 173,958