Share-Based Payment Awards - Deferred Stock Units - Additional Information (Detail) - shares	1 Months Ended	9 Months Ended
	Jan. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
2016 Long Term Incentive Plan [Member]
Class of Stock [Line Items]
Ratable annual vesting period of equity awards	4 years
Non Executive Directors [Member]
Class of Stock [Line Items]
Non-vested deferred stock units outstanding		0	35,418
Deferred Stock Units [Member]
Class of Stock [Line Items]
Non-vested deferred stock units outstanding			35,418
Ratable annual vesting period of equity awards		1 year
Deferred Stock Units [Member] | 2016 Long Term Incentive Plan [Member]
Class of Stock [Line Items]
Vested deferred stock units vested		71,251