Income per Common Share of the Trust - Share Repurchase (Details) - Common shares [Member] - 2015 Share Repurchase Program [Member] - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Jun. 30, 2016	Mar. 31, 2016
Class of Stock [Line Items]
Authorized amount of shares available to be repurchased under a share repurchase plan	$ 250.0
Number of shares repurchased during period	0.0	1.4
Amount paid for repurchase of shares		$ 40.9
Stock Acquired, Average Cost Per Share		$ 29.28