Stock-based Compensation Plans - PG/RG-PSUs Activities (Detail) - Performance-based PG-PSUs and RG-PSUs - $ / shares	12 Months Ended
	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding, Beginning Balance	536,798		122,921		0
Granted	345,202	[1]	440,938	[1]	122,921
Forfeited	(427)		(27,061)	[2]
Outstanding, Ending Balance	881,573		536,798		122,921
Outstanding, Beginning Balance, weighted average grant date fair value	$ 15.61		$ 25.53		$ 0
Granted, weighted average grant date fair value	10.32	[1]	15.22	[1]	25.53
Forfeited, weighted average grant date fair value	15.65		23.03	[2]
Outstanding, Ending Balance, weighted average grant date fair value	$ 11.70		$ 15.61		$ 25.53

[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] The first of three tranches of PG-PSUs granted in 2017 was forfeited as the performance metric was not met.