Stock-based Compensation Plans - Internal Performance Activities (Detail) - Performance-based Internal Performance Awards	3 Months Ended
	Mar. 31, 2021 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding, Beginning Balance | shares	1,099,102
Granted | shares	303,231	[1]
Vested | shares	(306,978)	[2]
Outstanding, Ending Balance | shares	1,095,355
Outstanding, Beginning Balance, weighted average grant date fair value | $ / shares	$ 5.92
Granted, weighted average grant date fair value | $ / shares	9.81	[1]
Vested, weighted average grant date fair value | $ / shares	12.20	[2]
Outstanding, Ending Balance, weighted average grant date fair value | $ / shares	$ 7.80

[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 certain of the PS-PSUs and RS-PSUs awards issued during 2018 the aggregate payout was approximately 137% of target for the March 2018 grants with a positive performance adjustment of 290,140 shares