Share-Based Payment Awards - Deferred Stock Units - Additional Information (Detail) - shares	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Non Executive Directors [Member]
Class of Stock [Line Items]
Non-vested deferred stock units outstanding	417	35,418
Deferred Stock Units [Member]
Class of Stock [Line Items]
Non-vested deferred stock units outstanding	417	35,418
Ratable annual vesting period of equity awards	1 year
Weighted average remaining vesting term	2 months 9 days
Deferred Stock Units [Member] | 2016 Long Term Incentive Plan [Member]
Class of Stock [Line Items]
Vested deferred stock units vested	70,834