Shareholders' Equity / Partners' Capital - Participating Preferred Shares (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Class of Stock [Line Items]
Preferred shares, shares outstanding (in shares)	35,350,000		35,350,000
Liquidation Value	$ 883,750		$ 883,750
Series D Perpetual Preferred Shares/Units
Class of Stock [Line Items]
Preferred stock, dividend rate, percentage	6.50%	6.50%
Preferred shares, shares outstanding (in shares)	10,750,000		10,750,000
Liquidation Value	$ 268,750		$ 268,750
Series E Perpetual Preferred Shares
Class of Stock [Line Items]
Preferred stock, dividend rate, percentage	6.35%	6.35%
Preferred shares, shares outstanding (in shares)	9,200,000		9,200,000
Liquidation Value	$ 230,000		$ 230,000
Series F Perpetual Preferred Shares
Class of Stock [Line Items]
Preferred stock, dividend rate, percentage	5.875%	5.875%
Preferred shares, shares outstanding (in shares)	6,200,000		6,200,000
Liquidation Value	$ 155,000		$ 155,000
Series G Perpetual Preferred Shares
Class of Stock [Line Items]
Preferred stock, dividend rate, percentage	5.875%	5.875%
Preferred shares, shares outstanding (in shares)	4,600,000		4,600,000
Liquidation Value	$ 115,000		$ 115,000
Series H Perpetual Preferred Shares
Class of Stock [Line Items]
Preferred stock, dividend rate, percentage	6.25%
Preferred shares, shares outstanding (in shares)	4,600,000		4,600,000
Liquidation Value	$ 115,000		$ 115,000