Stock-Based Compensation - Summary of Stock-based Awards for 2008 Plan and 2015 Plan (Detail) - 2008 Plan and 2015 Plan [Member] - shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock Options, Outstanding at beginning balance	3,077,264	1,916,832
Stock Options, Granted	90,000	10,000
Stock Options, Exercised	(23,593)	(37,894)
Stock Options, Forfeited	(9,844)	(102,500)
Stock Options, Outstanding at ending balance	3,133,827	1,786,438
RSUs, Outstanding at beginning balance	156,250	86,875
RSUs, Granted		120,000
RSUs, Exercised	(13,125)	(11,250)
RSUs, Outstanding at ending balance	143,125	195,625
Total, Outstanding at beginning balance	3,233,514	2,003,707
Total, Granted	90,000	130,000
Total, Exercised	(36,718)	(49,144)
Total, Forfeited	(9,844)	(102,500)
Total, Outstanding at ending balance	3,276,952	1,982,063