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		Dec. 31, 2020	Dec. 31, 2019	Aug. 06, 2019	[2]	Aug. 05, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Aggregate grant date fair value of restricted stock units issued						$ 0.3
Grant Date Market Price						$ 6.95
Unvested awards converted into newly issued TSUs	[1]	$ 5.12	$ 5.12	$ 5.12		$ 8.35	$ 11.36

[1] Determined by dividing the aggregate grant date fair value of awards by the number of awards issued.

[2] This reflects the unvested Board RSU awards converted into newly issued Board RSUs at August 6, 2019 in which the stock price was at $5.12 per share.