Shareholders' Equity, Noncontrolling Interests and Other Comprehensive Income - Common Shares and Units - Additional Information (Details) - USD ($) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	May 10, 2017	May 09, 2017
Class of Stock [Line Items]
Common shares, authorized (in shares)	200,000,000		200,000,000	200,000,000	100,000,000
Restricted shares
Class of Stock [Line Items]
Restricted stock, shares canceled for tax withholding for share based compensation (in shares)	3,288		4,314
LTIP Units and Restricted Stock
Class of Stock [Line Items]
Unit based compensation	$ 6.3	$ 6.5	$ 8.4