Stock-based Compensation Plans - PS/RS-PSUs Activities (Detail) - Performance-based PS-PSUs and RS-PSUs	6 Months Ended
	Jun. 30, 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)	[2]
Outstanding, Ending Balance | shares	1,558,270
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	[2]
Outstanding, Ending Balance, weighted average grant date fair value | $ / shares	$ 4.86

[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 the PS-PSUs and RS-PSUs awards issued during 2017 the aggregate payout was approximately 150% of target for the March 2017 and May 2017 grants with a positive performance adjustment of 58,591 shares