Shareholders' Equity - Summary of Stock Option Activity (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Roll Forward
Number of Shares, Beginning Balance	1,912,161	1,846,768
Granted, Number of Shares	316,393	248,100
Exercised, Number of Shares	(2,422)	(54,692)
Forfeited, Number of Shares	(434,374)	(91,411)
Expired, Number of Shares	(401,746)	(36,604)
Number of Shares, Ending Balance	1,390,012	1,912,161	1,846,768
Vested and expected to vest, Number of Shares, Ending Balance	1,293,384
Exercisable, Number of Shares, Ending Balance	929,224
Weighted Average Exercise Price, Beginning Balance	$ 4.88	$ 4.84
Granted, Weighted Average Exercise Price	3.63	5.18
Exercised, Weighted Average Exercise Price	3.59	3.66
Forfeited, Weighted Average Exercise Price	4.88	5.31
Expired, Weighted Average Exercise Price	4.27	5.83
Weighted Average Exercise Price, Ending Balance	4.77	$ 4.88	$ 4.84
Vested and expected to vest, Weighted Average Exercise Price, Ending Balance	4.79
Exercisable, Weighted Average Exercise Price, Ending Balance	$ 4.86
Weighted Average Remaining Contractual Life (in years)	6 years 9 months 29 days	7 years 7 months 9 days	8 years 2 months 8 days
Vested and expected to vest, Weighted Average Remaining Contractual Life (in years)	6 years 8 months 12 days
Exercisable, Weighted Average Remaining Contractual Life (in years)	6 years 18 days