Stock-based Compensation Plans - PG/RG-PSUs Activities (Detail) - Performance-based PG-PSUs and RG-PSUs	3 Months Ended
	Mar. 31, 2019 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding, Beginning Balance | shares	536,798
Granted | shares	345,202	[1]
Outstanding, Ending Balance | shares	882,000
Outstanding, Beginning Balance, weighted average grant date fair value | $ / shares	$ 15.61
Granted, weighted average grant date fair value | $ / shares	10.32	[1]
Outstanding, Ending Balance, weighted average grant date fair value | $ / shares	$ 11.70

[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