Shareholders' Equity - Summary of Stock Option Activity (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 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	170,643
Exercised, Number of Shares	(680)
Forfeited, Number of Shares	(11,100)
Expired, Number of Shares	(13,556)
Number of Shares, Ending Balance	2,057,468	1,912,161
Vested and expected to vest, Number of Shares, Ending Balance	1,924,493
Exercisable, Number of Shares, Ending Balance	1,127,389
Weighted Average Exercise Price, Beginning Balance	$ 4.88
Granted, Weighted Average Exercise Price	4.16
Exercised, Weighted Average Exercise Price	3.62
Forfeited, Weighted Average Exercise Price	5.28
Expired, Weighted Average Exercise Price	5.78
Weighted Average Exercise Price, Ending Balance	4.81	$ 4.88
Vested and expected to vest, Weighted Average Exercise Price, Ending Balance	4.80
Exercisable, Weighted Average Exercise Price, Ending Balance	$ 4.55
Weighted Average Remaining Contractual Life (in years)	7 years 7 months 2 days	7 years 7 months 9 days
Vested and expected to vest, Weighted Average Remaining Contractual Life (in years)	7 years 5 months 26 days
Exercisable, Weighted Average Remaining Contractual Life (in years)	6 years 6 months 14 days
Balance outstanding, Aggregate Intrinsic Value	$ 559,221	$ 781,735
Vested and expected to vest, Aggregate Intrinsic Value	554,722
Exercisable, Aggregate Intrinsic Value	$ 534,925