Share-Based Payment Awards - Stock Options - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2019 shares
2016 Long Term Incentive Plan [Member]
Class of Stock [Line Items]
Contractual life of option grants	10 years
Stock Compensation Plan [Member]
Class of Stock [Line Items]
Common stock vested during the period	1,212,780
Employees [Member]
Class of Stock [Line Items]
Options granted	13,500
Ratable annual vesting period	3 years
Employees [Member] | 2016 Long Term Incentive Plan [Member]
Class of Stock [Line Items]
Options granted	2,892,060
Ratable monthly vesting period	4 years
Employees [Member] | Stock Compensation Plan [Member]
Class of Stock [Line Items]
Options granted	788,000
Ratable monthly vesting period	1 year
Cliff vesting period	3 years
Newly Appointed Non Executive Director [Member]
Class of Stock [Line Items]
Options granted	80,000
Ratable annual vesting period	3 years
Directors and External consultants [Member]
Class of Stock [Line Items]
Options granted	388,536
Cliff vesting period	1 year