Ordinary and Preference Shares - Summary of Shares Issued and Outstanding (Detail) - $ / shares	Dec. 31, 2019	Sep. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Mar. 31, 2018
Class Of Stock [Line Items]
Ordinary shares, shares issued	80,256,946		65,900,447
Ordinary shares, shares outstanding	80,256,946		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	$ 30.24		$ 29.06
Ordinary Shares [Member]
Class Of Stock [Line Items]
Ordinary shares, shares issued	80,256,946		65,900,447
Ordinary shares, shares outstanding	80,256,946	66,366,706	65,900,447	64,972,552	54,229,503	45,646,424
Ordinary shares, par value