Shareholders' Equity - Distributions (Details) - $ / shares	1 Months Ended			3 Months Ended		9 Months Ended
	Jul. 31, 2016	Jun. 30, 2016	May 31, 2016	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Class of Stock [Line Items]
Common stock dividend declared (in USD per share)				$ 0.05	$ 0.05	$ 0.15	$ 0.15
Class A common shares
Class of Stock [Line Items]
Common stock dividend declared (in USD per share)				0.05	0.05
Class B common shares
Class of Stock [Line Items]
Common stock dividend declared (in USD per share)				$ 0.05	0.05
5.0% Series A Participating Preferred Shares
Class of Stock [Line Items]
Preferred stock, dividend rate, percentage				5.00%		5.00%	5.00%
Preferred stock dividends declared (in USD per share)				$ 0.3125	0.3125
5.0% Series B Participating Preferred Shares
Class of Stock [Line Items]
Preferred stock, dividend rate, percentage				5.00%		5.00%	5.00%
Preferred stock dividends declared (in USD per share)				$ 0.3125	0.3125
5.5% Series C Participating Preferred Shares
Class of Stock [Line Items]
Preferred stock, dividend rate, percentage				5.50%		5.50%	5.50%
Preferred stock dividends declared (in USD per share)				$ 0.34375	0.34375
Series D Preferred Shares
Class of Stock [Line Items]
Preferred stock, dividend rate, percentage			6.50%	6.50%		6.50%
Preferred stock dividends declared (in USD per share)				$ 0.40625
Series E Perpetual Preferred Shares
Class of Stock [Line Items]
Preferred stock, dividend rate, percentage	6.35%	6.35%		6.35%		6.35%
Preferred stock dividends declared (in USD per share)				$ 0.40569
Series D Convertible Units
Class of Stock [Line Items]
Declared distributions (in USD per share)				0.035		$ 0.035
Series C Convertible Units
Class of Stock [Line Items]
Declared distributions (in USD per share)				$ 0	$ 0.15113	$ 0	$ 0.15113
Series D Convertible Units
Class of Stock [Line Items]
Percentage of participation eligibility on distributions						70.00%