Shareholders' Equity - Summary of Stock Option Activity (Detail) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Roll Forward
Number of Shares, Beginning Balance	1,390,012
Granted, Number of Shares	933,423
Forfeited, Number of Shares	(218,889)
Expired, Number of Shares	(467,490)
Number of Shares, Ending Balance	1,637,056	1,390,012
Vested and expected to vest, Number of Shares, Ending Balance	1,349,818
Exercisable, Number of Shares, Ending Balance	596,324
Weighted Average Exercise Price, Beginning Balance	$ 4.77
Granted, Weighted Average Exercise Price	1.70
Forfeited, Weighted Average Exercise Price	4.98
Expired, Weighted Average Exercise Price	5.00
Weighted Average Exercise Price, Ending Balance	2.93	$ 4.77
Vested and expected to vest, Weighted Average Exercise Price, Ending Balance	3.17
Exercisable, Weighted Average Exercise Price, Ending Balance	$ 4.69
Weighted Average Remaining Contractual Life (in years)	7 years 8 months 1 day	6 years 9 months 29 days
Vested and expected to vest, Weighted Average Remaining Contractual Life (in years)	7 years 3 months 10 days
Exercisable, Weighted Average Remaining Contractual Life (in years)	4 years 8 months 1 day
Balance outstanding, Aggregate Intrinsic Value	$ 505
Vested and expected to vest, Aggregate Intrinsic Value	$ 343