Stock-based Compensation Plans - PG/RG-PSUs Activities (Detail) - Performance-based PG-PSUs and RG-PSUs	12 Months Ended
	Dec. 31, 2020 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding, Beginning Balance | shares	881,573
Granted | shares	777,847	[1]
Vested | shares	(101,150)
Forfeited | shares	(459,168)	[2]
Outstanding, Ending Balance | shares	1,099,102
Outstanding, Beginning Balance, weighted average grant date fair value | $ / shares	$ 11.70
Granted, weighted average grant date fair value | $ / shares	2.33	[1]
Vested, weighted average grant date fair value | $ / shares	15.32
Forfeited, weighted average grant date fair value | $ / shares	2.33	[2]
Outstanding, Ending Balance, weighted average grant date fair value | $ / shares	$ 5.92

[1] Amounts granted reflect the number of performance units granted; however, the actual payout of shares will be between zero and 200% depending on achievement of specifically identified performance targets.

[2] For RG-PSU’s tranches granted in 2018, 2019 and 2020 which are set to vest in early 2021, the performance metric is not expected to be met and are considered forfeited. For PG-PSU’s tranches granted in 2018, 2019 and 2020 which are set to vest in early 2021, the payout is estimated at 23% with the remainder considered to be forfeited.