Option Activity under Stock-Based Compensation Plans (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) $ / shares shares
Shares Underlying Outstanding Options
Beginning balance | shares	3,975
Options granted | shares	155
Ending balance | shares	3,799
Vested and expected to vest at March 31, 2017 | shares	3,785
Exercisable at March 31, 2017 | shares	2,181
Weighted-Average Exercise Price Per Share
Beginning balance | $ / shares	$ 21.38
Options granted | $ / shares	6.24
Ending balance | $ / shares	20.65
Vested and expected to vest at March 31, 2017 | $ / shares	20.67
Exercisable at March 31, 2017 | $ / shares	$ 22.93
Weighted-Average Remaining Contractual Term (years)
Balance at March 31, 2017	6 years 1 month 28 days
Vested and expected to vest at March 31, 2017	6 years 1 month 24 days
Exercisable at March 31, 2017	5 years 4 months 28 days
Aggregate Intrinsic Value
Balance at March 31, 2017 | $	$ 42
Vested and expected to vest at March 31, 2017 | $	42
Exercisable at March 31, 2017 | $	$ 19
Unvested
Shares Underlying Outstanding Options
Options cancelled | shares	(279)
Weighted-Average Exercise Price Per Share
Options cancelled | $ / shares	$ 18.50
Vested
Shares Underlying Outstanding Options
Options cancelled | shares	(52)
Weighted-Average Exercise Price Per Share
Options cancelled | $ / shares	$ 44.32