Subsequent Events - Declaration of Dividends (Details) - $ / shares		1 Months Ended			3 Months Ended		9 Months Ended
	Nov. 01, 2016	Jul. 31, 2016	Jun. 30, 2016	May 31, 2016	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Subsequent Event [Line Items]
Quarterly dividend (in USD per share)					$ 0.05	$ 0.05	$ 0.15	$ 0.15
Class A common shares
Subsequent Event [Line Items]
Quarterly dividend (in USD per share)					0.05	0.05
Class B common shares
Subsequent Event [Line Items]
Quarterly dividend (in USD per share)					0.05	0.05
5.0% Series A Participating Preferred Shares
Subsequent Event [Line Items]
Quarterly preferred dividend (in USD per share)					$ 0.3125	0.3125
Preferred stock, dividend rate, percentage					5.00%		5.00%	5.00%
5.0% Series B Participating Preferred Shares
Subsequent Event [Line Items]
Quarterly preferred dividend (in USD per share)					$ 0.3125	0.3125
Preferred stock, dividend rate, percentage					5.00%		5.00%	5.00%
5.5% Series C Participating Preferred Shares
Subsequent Event [Line Items]
Quarterly preferred dividend (in USD per share)					$ 0.34375	$ 0.34375
Preferred stock, dividend rate, percentage					5.50%		5.50%	5.50%
Series D Perpetual Preferred Shares
Subsequent Event [Line Items]
Quarterly preferred dividend (in USD per share)					$ 0.40625
Preferred stock, dividend rate, percentage				6.50%	6.50%		6.50%
Series E Perpetual Preferred Shares
Subsequent Event [Line Items]
Quarterly preferred dividend (in USD per share)					$ 0.40569
Preferred stock, dividend rate, percentage		6.35%	6.35%		6.35%		6.35%
Subsequent Event | Class A common shares
Subsequent Event [Line Items]
Quarterly dividend (in USD per share)	$ 0.05
Subsequent Event | Class B common shares
Subsequent Event [Line Items]
Quarterly dividend (in USD per share)	0.05
Subsequent Event | 5.0% Series A Participating Preferred Shares
Subsequent Event [Line Items]
Quarterly preferred dividend (in USD per share)	$ 0.3125
Subsequent Event | 5.0% Series A Participating Preferred Shares | Dividend Declared
Subsequent Event [Line Items]
Preferred stock, dividend rate, percentage	5.00%
Subsequent Event | 5.0% Series B Participating Preferred Shares
Subsequent Event [Line Items]
Quarterly preferred dividend (in USD per share)	$ 0.3125
Subsequent Event | 5.0% Series B Participating Preferred Shares | Dividend Declared
Subsequent Event [Line Items]
Preferred stock, dividend rate, percentage	5.00%
Subsequent Event | 5.5% Series C Participating Preferred Shares
Subsequent Event [Line Items]
Quarterly preferred dividend (in USD per share)	$ 0.34375
Subsequent Event | 5.5% Series C Participating Preferred Shares | Dividend Declared
Subsequent Event [Line Items]
Preferred stock, dividend rate, percentage	5.50%
Subsequent Event | Series D Perpetual Preferred Shares
Subsequent Event [Line Items]
Quarterly preferred dividend (in USD per share)	$ 0.40625
Preferred stock, dividend rate, percentage	6.50%
Subsequent Event | Series E Perpetual Preferred Shares
Subsequent Event [Line Items]
Quarterly preferred dividend (in USD per share)	$ 0.39688
Preferred stock, dividend rate, percentage	6.35%