Share-Based Payments - Summary of Stock Option Activity (Detail)	3 Months Ended
	Mar. 31, 2018 $ / shares shares
Shares
Outstanding at beginning of period (in shares) | shares	2,695,796
Granted (in shares) | shares	102,500
Exercised (in shares) | shares	0
Cancelled or forfeited (in shares) | shares	(150,292)
Outstanding at end of period (in shares) | shares	2,648,004
Exercisable at end of period (in shares) | shares	1,580,060
Vested and expected to vest at end of period (in shares) | shares	2,586,804
Weighted-Average Exercise Price
Outstanding at beginning of period (in USD per share) | $ / shares	$ 3.16
Granted (in USD per share) | $ / shares	0.93
Exercised (in USD per share) | $ / shares	0.00
Cancelled or forfeited (in USD per share) | $ / shares	2.20
Outstanding at end of period (in USD per share) | $ / shares	3.13
Exercisable at end of period (in USD per share) | $ / shares	3.79
Vested and expected to vest at end of period (in USD per share) | $ / shares	$ 3.16