Common Shares - Additional Information (Detail) - $ / shares	Dec. 31, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Common shares, outstanding	36,425,084	36,425,084
Trust [Member]
Class of Stock [Line Items]
Common shares, par value	$ 1
Common shares, issued	36,425,084	36,425,084
Common shares, outstanding	36,425,084	36,425,084