Ordinary and Preference Shares - Summary of Shares Issued and Outstanding (Detail) - $ / shares	Sep. 30, 2017	Mar. 31, 2017
Class Of Stock [Line Items]
Ordinary shares, shares issued	37,694,531	29,567,698
Ordinary shares, shares outstanding	37,694,531	29,567,698
Ordinary shares, par value
Preference shares, shares issued	666,665	666,665
Preference shares, shares outstanding	666,665	666,665
Ordinary Shares [Member]
Class Of Stock [Line Items]
Ordinary shares, shares issued	37,694,531	29,567,698
Ordinary shares, shares outstanding	37,694,531	29,567,698
Ordinary shares, par value
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	$ 26.71	$ 25.92