Shareholders' Equity / Partners' Capital - Distributions (Details) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Class of Stock [Line Items]
Common stock dividend declared (in dollars per share)	$ 0.05	$ 0.05	$ 0.15	$ 0.15
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
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%	6.50%	6.50%
Series E Perpetual Preferred Shares
Class of Stock [Line Items]
Preferred stock dividends declared (in dollars per share)	$ 0.40	$ 0.40
Preferred stock, dividend rate, percentage	6.35%	6.35%	6.35%
Series F Perpetual Preferred Shares
Class of Stock [Line Items]
Preferred stock dividends declared (in dollars per share)	$ 0.37	$ 0.37
Preferred stock, dividend rate, percentage	5.875%	5.875%	5.875%
Series G Perpetual Preferred Shares
Class of Stock [Line Items]
Preferred stock dividends declared (in dollars per share)	$ 0.37	$ 0.30
Preferred stock, dividend rate, percentage	5.875%		5.875%
Series H Perpetual Preferred Shares
Class of Stock [Line Items]
Preferred stock, dividend rate, percentage	6.25%		6.25%
5.0% Series A Participating Preferred Shares
Class of Stock [Line Items]
Preferred stock dividends declared (in dollars per share)		$ 0.31
Preferred stock, dividend rate, percentage		5.00%
5.0% Series B Participating Preferred Shares
Class of Stock [Line Items]
Preferred stock dividends declared (in dollars per share)		$ 0.31
Preferred stock, dividend rate, percentage		5.00%
5.5% Series C Participating Preferred Shares
Class of Stock [Line Items]
Preferred stock dividends declared (in dollars per share)		$ 0.34
Preferred stock, dividend rate, percentage		5.50%	5.50%