Shareholders' Equity / Partners' Capital - Distributions (Details) - $ / shares	3 Months Ended			9 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Class of Stock [Line Items]
Common stock dividend declared (in dollars per share)	$ 0.05		$ 0.05	$ 0.15	$ 0.15
Series D Convertible Units
Class of Stock [Line Items]
Preferred stock dividends declared (in dollars per share)			$ 0.04
Convertible units, percent of class A units (as a percent)			70.00%
Class A common shares/units
Class of Stock [Line Items]
Common stock dividend declared (in dollars per share)	0.05		$ 0.05
Class B common shares
Class of Stock [Line Items]
Common stock dividend declared (in dollars per share)	0.05		0.05
5.0% Series A Participating Preferred Shares
Class of Stock [Line Items]
Preferred stock dividends declared (in dollars per share)	$ 0.31		$ 0.31
Preferred stock, dividend rate, percentage	5.00%		5.00%	5.00%
5.0% Series B Participating Preferred Shares
Class of Stock [Line Items]
Preferred stock dividends declared (in dollars per share)	$ 0.31		$ 0.31
Preferred stock, dividend rate, percentage	5.00%		5.00%	5.00%
5.5% Series C Participating Preferred Shares
Class of Stock [Line Items]
Preferred stock dividends declared (in dollars per share)	$ 0.34		$ 0.34
Preferred stock, dividend rate, percentage	5.50%		5.50%	5.50%
Series D Perpetual Preferred Shares/Units
Class of Stock [Line Items]
Preferred stock dividends declared (in dollars per share)	$ 0.41		$ 0.41
Preferred stock, dividend rate, percentage	6.50%
Series E Perpetual Preferred Shares
Class of Stock [Line Items]
Preferred stock dividends declared (in dollars per share)	$ 0.40		$ 0.41
Preferred stock, dividend rate, percentage	6.35%
Series F Perpetual Preferred Shares
Class of Stock [Line Items]
Preferred stock dividends declared (in dollars per share)	$ 0.37
Preferred stock, dividend rate, percentage		5.875%
Series G, Preferred Perpetual Shares
Class of Stock [Line Items]
Preferred stock dividends declared (in dollars per share)	$ 0.30
Preferred stock, dividend rate, percentage	5.875%