Shareholders' Equity - Summary of Stock Option Activity (Detail) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Roll Forward
Number of Shares, Beginning Balance	1,912,161
Granted, Number of Shares	283,893
Exercised, Number of Shares	(2,422)
Forfeited, Number of Shares	(385,736)
Expired, Number of Shares	(332,036)
Number of Shares, Ending Balance	1,475,860	1,912,161
Vested and expected to vest, Number of Shares, Ending Balance	1,366,764
Exercisable, Number of Shares, Ending Balance	954,862
Weighted Average Exercise Price, Beginning Balance	$ 4.88
Granted, Weighted Average Exercise Price	3.78
Exercised, Weighted Average Exercise Price	3.59
Forfeited, Weighted Average Exercise Price	4.94
Expired, Weighted Average Exercise Price	4.17
Weighted Average Exercise Price, Ending Balance	4.81	$ 4.88
Vested and expected to vest, Weighted Average Exercise Price, Ending Balance	4.82
Exercisable, Weighted Average Exercise Price, Ending Balance	$ 4.84
Weighted Average Remaining Contractual Life (in years)	6 years 10 months 17 days	7 years 7 months 9 days
Vested and expected to vest, Weighted Average Remaining Contractual Life (in years)	6 years 8 months 23 days
Exercisable, Weighted Average Remaining Contractual Life (in years)	5 years 11 months 19 days
Balance outstanding, Aggregate Intrinsic Value	$ 3,950	$ 781,735
Vested and expected to vest, Aggregate Intrinsic Value	$ 3,259