Stock-Based Compensation - Summary of Stock-based Awards for 2008 Plan and 2015 Plan (Detail) - 2008 Plan and 2015 Plan [Member] - shares	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock Options, Outstanding at beginning balance	1,916,832	2,129,856
Stock Options, Granted	1,016,720	42,500
Stock Options, Exercised	(175,407)	(118,213)
Stock Options, Forfeited	(123,850)	(447,065)
Stock Options, Outstanding at ending balance	2,634,295	1,607,078
RSUs, Outstanding at beginning balance	86,875
RSUs, Granted	120,000	122,588
RSUs, Exercised	(37,500)	(72,361)
RSUs, Forfeited		(227)
RSUs, Outstanding at ending balance	169,375	50,000
Total, Outstanding at beginning balance	2,003,707	2,129,856
Total, Granted	1,136,720	165,088
Total, Exercised	(212,907)	(190,574)
Total, Forfeited	(123,850)	(447,292)
Total, Outstanding at ending balance	2,803,670	1,657,078