Equity-based Awards - Summary of Information Regarding Restricted Stock Awards (Parenthetical) (Detail) - Restricted Stock Units (RSUs) - 2017 Non-Employee Directors Compensation Plan [Member] - USD ($) $ / shares in Units, $ in Millions	Aug. 05, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Aggregate grant date fair value of restricted stock units issued	$ 0.3	$ 0.3	$ 0.2
Grant Date Market Price	$ 6.95	$ 10.45	$ 13.77