Summary of Warrant (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Shares [Abstract]
Number of warrants, Outstanding	3,648,541	0
Warrants assumed in the Merger		1,898,541
Warrants granted	0	1,750,000
Warrants exercised	(286,357)
Warrants forfeited	(30,189)
Number of warrants, Outstanding	3,331,995	3,648,541
Weighted Average Exercise Price [Abstract]
Warrants outstanding Balance	$ 9.75	$ 0
Warrants assumed in the Merger		9.06
Warrants granted	0	10.49
Warrants exercised	7.84
Warrants forfeited	4.50
Warrants outstanding Balance	$ 9.93	$ 9.75
Weighted Average Remaining Contractual Term Years [Abstract]
Warrants assumed in the Merger		2 years 8 months 8 days
Warrants granted		5 years
Warrants outstanding Balance	2 years 11 months 19 days	3 years 8 months 26 days
Aggregate Intrinsic Value [Abstract]
Warrants outstanding Balance	$ 33.1	$ 52.0	$ 0.0
Warrants assumed in the Merger		1.8
Warrants granted	0.0	$ 0.0
Warrants exercised	3.0
Warrants forfeited	$ 0.0