Ordinary and Preference Shares - Summary of Shares Issued and Outstanding (Detail) - $ / shares	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018
Class Of Stock [Line Items]
Ordinary shares, shares issued	66,212,893	65,900,447
Ordinary shares, shares outstanding	66,212,893	65,900,447
Ordinary shares, par value
Preference shares, shares issued	666,665	666,665
Preference shares, shares outstanding	666,665	666,665
7% Cumulative Redeemable Preference Shares [Member]
Class Of Stock [Line Items]
Preference shares, shares issued	666,665	666,665
Preference shares, shares outstanding	666,665	666,665
Liquidation amount per share	$ 29.46	$ 29.06
Ordinary Shares [Member]
Class Of Stock [Line Items]
Ordinary shares, shares issued	66,212,893	65,900,447
Ordinary shares, shares outstanding	66,212,893	65,900,447	46,064,701	45,646,424
Ordinary shares, par value