Share-based Payments - Summary of Share Options Outstanding (Parenthetical) (Detail)	Dec. 31, 2018 USD ($)
Bottom Of Range [Member] \| 1.65 to 45.00
Disclosure Of Share Based Payments [Line Items]
Weighted average exercise price	$ 1.65
Bottom Of Range [Member] \| 45.01 to 90.00
Disclosure Of Share Based Payments [Line Items]
Weighted average exercise price	45.01
Bottom Of Range [Member] \| 90.01 to 135.00
Disclosure Of Share Based Payments [Line Items]
Weighted average exercise price	90.01
Bottom Of Range [Member] \| 135.01 to 180.00
Disclosure Of Share Based Payments [Line Items]
Weighted average exercise price	135.01
Bottom Of Range [Member] \| 180.01 to 189.52
Disclosure Of Share Based Payments [Line Items]
Weighted average exercise price	180.01
Top of range \| 1.65 to 45.00
Disclosure Of Share Based Payments [Line Items]
Weighted average exercise price	45.00
Top of range \| 45.01 to 90.00
Disclosure Of Share Based Payments [Line Items]
Weighted average exercise price	90.00
Top of range \| 90.01 to 135.00
Disclosure Of Share Based Payments [Line Items]
Weighted average exercise price	135.00
Top of range \| 135.01 to 180.00
Disclosure Of Share Based Payments [Line Items]
Weighted average exercise price	180.00
Top of range \| 180.01 to 189.52
Disclosure Of Share Based Payments [Line Items]
Weighted average exercise price	$ 189.52