Subsequent Events - Declaration of Dividends (Details) - $ / shares		3 Months Ended			9 Months Ended
	Nov. 02, 2017	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Subsequent Event [Line Items]
Quarterly dividend (in dollars per share)		$ 0.05		$ 0.05	$ 0.15	$ 0.15
Class A common shares/units
Subsequent Event [Line Items]
Quarterly dividend (in dollars per share)		0.05		0.05
Class B common shares
Subsequent Event [Line Items]
Quarterly dividend (in dollars per share)		0.05		0.05
5.5% Series C Participating Preferred Shares
Subsequent Event [Line Items]
Quarterly preferred dividend (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
Subsequent Event [Line Items]
Quarterly preferred dividend (in dollars per share)		$ 0.41		$ 0.41
Preferred stock, dividend rate, percentage		6.50%
Series E Perpetual Preferred Shares
Subsequent Event [Line Items]
Quarterly preferred dividend (in dollars per share)		$ 0.40		$ 0.41
Preferred stock, dividend rate, percentage		6.35%
Series F Perpetual Preferred Shares
Subsequent Event [Line Items]
Quarterly preferred dividend (in dollars per share)		$ 0.37
Preferred stock, dividend rate, percentage			5.875%
Series G, Preferred Perpetual Shares
Subsequent Event [Line Items]
Quarterly preferred dividend (in dollars per share)		$ 0.30
Preferred stock, dividend rate, percentage		5.875%
Subsequent Event | Class A common shares/units | Dividend Declared
Subsequent Event [Line Items]
Quarterly dividend (in dollars per share)	$ 0.05
Subsequent Event | 5.5% Series C Participating Preferred Shares | Dividend Declared
Subsequent Event [Line Items]
Quarterly preferred dividend (in dollars per share)	$ 0.34375
Preferred stock, dividend rate, percentage	5.50%
Subsequent Event | Series D Perpetual Preferred Shares/Units | Dividend Declared
Subsequent Event [Line Items]
Quarterly preferred dividend (in dollars per share)	$ 0.40625
Preferred stock, dividend rate, percentage	6.50%
Subsequent Event | Series E Perpetual Preferred Shares | Dividend Declared
Subsequent Event [Line Items]
Quarterly preferred dividend (in dollars per share)	$ 0.39688
Preferred stock, dividend rate, percentage	6.35%
Subsequent Event | Series F Perpetual Preferred Shares | Dividend Declared
Subsequent Event [Line Items]
Quarterly preferred dividend (in dollars per share)	$ 0.36719
Preferred stock, dividend rate, percentage	5.875%
Subsequent Event | Series G, Preferred Perpetual Shares | Dividend Declared
Subsequent Event [Line Items]
Quarterly preferred dividend (in dollars per share)	$ 0.36719
Preferred stock, dividend rate, percentage	5.875%