Shareholders' Equity - Summary of Stock Option Activity (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Roll Forward
Number of Shares, Beginning Balance	1,390,012	1,912,161
Granted, Number of Shares	958,798	316,393
Exercised, Number of Shares		(2,422)
Forfeited, Number of Shares	(251,213)	(434,374)
Expired, Number of Shares	(552,771)	(401,746)
Number of Shares, Ending Balance	1,544,826	1,390,012	1,912,161
Vested and expected to vest, Number of Shares, Ending Balance	1,278,079
Exercisable, Number of Shares, Ending Balance	525,289
Weighted Average Exercise Price, Beginning Balance	$ 4.77	$ 4.88
Granted, Weighted Average Exercise Price	1.69	3.63
Exercised, Weighted Average Exercise Price		3.59
Forfeited, Weighted Average Exercise Price	4.81	4.88
Expired, Weighted Average Exercise Price	5.07	4.27
Weighted Average Exercise Price, Ending Balance	2.74	$ 4.77	$ 4.88
Vested and expected to vest, Weighted Average Exercise Price, Ending Balance	2.95
Exercisable, Weighted Average Exercise Price, Ending Balance	$ 4.52
Weighted Average Remaining Contractual Life (in years)	7 years 5 months 19 days	6 years 9 months 29 days	7 years 7 months 9 days
Vested and expected to vest, Weighted Average Remaining Contractual Life (in years)	7 years 14 days
Exercisable, Weighted Average Remaining Contractual Life (in years)	3 years 11 months 1 day
Balance outstanding, Aggregate Intrinsic Value	$ 46,582
Vested and expected to vest, Aggregate Intrinsic Value	32,307
Exercisable, Aggregate Intrinsic Value	$ 31