Ordinary and Preference Shares - Additional Information (Detail) - USD ($) $ in Thousands	May 31, 2019	Jun. 30, 2019	Mar. 31, 2019
Class Of Stock [Line Items]
Aggregate amount of shares issued		$ 369,021	$ 368,958
Shares issued par value per share
Ordinary Shares [Member]
Class Of Stock [Line Items]
Shares issued par value per share
Open Market Sale Agreement [Member] | Jefferies LLC [Member] | Ordinary Shares [Member]
Class Of Stock [Line Items]
Aggregate amount of shares issued	$ 80,000
Shares issued par value per share
Commission on gross proceeds of shares sold, percentage	3.00%