Stock-Based Compensation - Summary of Stock Option Activity (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 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	19,024
Number of Options, Granted | shares	19,388
Number of Options, Exercised | shares	(2,562)
Number of Options, Forfeited | shares	(16,935)
Number of Options, Outstanding, Ending balance | shares	18,915	19,024
Number of Options, Vested and expected to vest | shares	18,870
Number of Options, Exercisable | shares	12,560
Weighted-Average Exercise Price, Outstanding, Beginning balance | $ / shares	$ 5.77
Weighted-Average Exercise Price, Granted | $ / shares	2.46
Weighted-Average Exercise Price, Exercised | $ / shares	2.29
Weighted-Average Exercise Price, Forfeited | $ / shares	6.24
Weighted-Average Exercise Price, Outstanding, Ending balance | $ / shares	2.43	$ 5.77
Weighted-Average Exercise Price, Vested and expected to vest | $ / shares	2.43
Weighted-Average Exercise Price, Exercisable | $ / shares	$ 2.81
Weighted-Average Remaining Contractual Term	5 years 10 months 14 days	5 years 11 months 19 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest	5 years 10 months 10 days
Weighted-Average Remaining Contractual Term, Exercisable	3 years 11 months 23 days
Aggregate Intrinsic Value, Outstanding | $	$ 440	$ 7,564
Aggregate Intrinsic Value, Vested and expected to vest | $	440
Aggregate Intrinsic Value, Exercisable | $	$ 440