Shareholders' Equity - Summary of Stock Option Activity (Detail) - $ / shares	6 Months Ended	12 Months Ended
	Jun. 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	676,500
Forfeited, Number of Shares	(181,995)
Expired, Number of Shares	(145,433)
Number of Shares, Ending Balance	1,739,084	1,390,012
Vested and expected to vest, Number of Shares, Ending Balance	1,502,904
Exercisable, Number of Shares, Ending Balance	893,634
Weighted Average Exercise Price, Beginning Balance	$ 4.77
Granted, Weighted Average Exercise Price	1.88
Forfeited, Weighted Average Exercise Price	4.85
Expired, Weighted Average Exercise Price	4.34
Weighted Average Exercise Price, Ending Balance	3.67	$ 4.77
Vested and expected to vest, Weighted Average Exercise Price, Ending Balance	3.91
Exercisable, Weighted Average Exercise Price, Ending Balance	$ 4.92
Weighted Average Remaining Contractual Life (in years)	6 years 5 months 26 days	6 years 9 months 29 days
Vested and expected to vest, Weighted Average Remaining Contractual Life (in years)	6 years
Exercisable, Weighted Average Remaining Contractual Life (in years)	3 years 8 months 19 days