Shareholders' Equity, Noncontrolling Interests and Other Comprehensive Income - Common Shares, Share Repurchases, Dividends and Distributions (Details) - USD ($)				3 Months Ended	6 Months Ended		12 Months Ended
	May 11, 2018	Feb. 27, 2018	Nov. 08, 2017	Jun. 30, 2018	Jun. 30, 2018	Jun. 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	200,000,000	100,000,000
Authorized amount				$ 200,000,000.0	$ 200,000,000.0
Number of shares repurchased during period (in shares)				990,041	2,294,235		0
Shares repurchased during period				$ 23,100,000	$ 55,057,000
Stock repurchase fees					100,000
Remaining authorized repurchase amount				$ 145,000,000	$ 145,000,000
Cash dividends declared per common share (in dollars per share)					$ 0.54	$ 0.52
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					$ 4,300,000		$ 8,400,000
Regular Quarterly Cash Dividend
Class of Stock [Line Items]
Cash dividends declared per common share (in dollars per share)	$ 0.27	$ 0.27	$ 0.27
Cash dividends declared, period increase (in dollars per share)			$ 0.01