Stockholders' equity - Schedule of Stock Option Transactions and Number of Stock Options Outstanding (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options Outstanding, Number of Shares, beginning balance	5,840,538
Options granted, Number of Shares	290,700
Options exercised, Number of Shares	(376,311)
Options forfeited, Number of Shares	(410,000)
Options Outstanding, Number of Shares, ending balance	5,344,927	5,840,538
Exercisable, Number of Shares, ending balance	1,040,512
Options Outstanding, Weighted Average Exercise Price, beginning balance	$ 5.11
Options granted, Weighted Average Exercise Price	7.63
Options exercised, Weighted Average Exercise Price	9.03
Options forfeited, Weighted Average Exercise Price	16.91
Options Outstanding, Weighted Average Exercise Price, ending balance	4.06	$ 5.11
Exercisable, Weighted Average Exercise Price, ending balance	$ 7.28
Options Outstanding, Weighted Average Remaining Contractual Life (Years), ending balance	8 years 8 months 12 days	7 years 8 months 19 days
Exercisable, Weighted Average Remaining Contractual Life (Years), ending balance	5 years 6 months 21 days
Options Outstanding, Aggregate Intrinsic Value	$ 40,431	$ 45,037
Exercisable, Aggregate Intrinsic Value	$ 5,462