Stock-Based Compensation - Summary of Stock Option Activity (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Roll Forward
Number of Options, Outstanding, Beginning balance | shares	1,902
Number of Options, Granted | shares	2,098
Number of Options, Exercised | shares	(290)
Number of Options, Forfeited | shares	(1,886)
Number of Options, Outstanding, Ending balance | shares	1,824	1,902
Number of Options, Vested and expected to vest | shares	1,822
Number of Options, Exercisable | shares	1,159
Weighted-Average Exercise Price, Outstanding, Beginning balance | $ / shares	$ 57.68
Weighted-Average Exercise Price, Granted | $ / shares	23.77
Weighted-Average Exercise Price, Exercised | $ / shares	21.74
Weighted-Average Exercise Price, Forfeited | $ / shares	59.37
Weighted-Average Exercise Price, Outstanding, Ending balance | $ / shares	22.65	$ 57.68
Weighted-Average Exercise Price, Vested and expected to vest | $ / shares	22.64
Weighted-Average Exercise Price, Exercisable | $ / shares	$ 26.71
Weighted-Average Remaining Contractual Term	6 years 2 months 16 days	5 years 11 months 19 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest	6 years 2 months 16 days
Weighted-Average Remaining Contractual Term, Exercisable	4 years 4 months 2 days
Aggregate Intrinsic Value, Outstanding | $	$ 1,187	$ 7,564
Aggregate Intrinsic Value, Vested and expected to vest | $	1,187
Aggregate Intrinsic Value, Exercisable | $	$ 969