Shareholders' Equity / Partners' Capital - Participating Preferred Shares (Details) $ / shares in Units, $ in Thousands		3 Months Ended			9 Months Ended
	Apr. 05, 2018 market shares	Sep. 30, 2018 USD ($) $ / shares shares	Jun. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) market $ / shares shares	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) $ / shares shares
Class of Stock [Line Items]
Preferred shares, shares outstanding (in shares) | shares		35,350,000			35,350,000		38,350,000
Liquidation Value		$ 883,750			$ 883,750		$ 986,986
Liquidation value (in dollars per share) | $ / shares		$ 25.00			$ 25.00
Number of top markets used for purchase price index | market					20
Redemption of participating preferred shares/units		$ 0		$ 0	$ 32,215	$ 0
5.5% Series C Participating Preferred Shares
Class of Stock [Line Items]
Preferred stock, dividend rate, percentage				5.50%	5.50%
Preferred shares, shares outstanding (in shares) | shares		0			0		7,600,000
Liquidation Value		$ 0			$ 0		$ 218,236
Stock converted during period (in shares) | shares	7,600,000
Series D Perpetual Preferred Shares/Units
Class of Stock [Line Items]
Preferred stock, dividend rate, percentage		6.50%		6.50%	6.50%
Preferred shares, shares outstanding (in shares) | shares		10,750,000			10,750,000		10,750,000
Liquidation Value		$ 268,750			$ 268,750		$ 268,750
Series E Perpetual Preferred Shares
Class of Stock [Line Items]
Preferred stock, dividend rate, percentage		6.35%		6.35%	6.35%
Preferred shares, shares outstanding (in shares) | shares		9,200,000			9,200,000		9,200,000
Liquidation Value		$ 230,000			$ 230,000		$ 230,000
Series F Perpetual Preferred Shares
Class of Stock [Line Items]
Preferred stock, dividend rate, percentage		5.875%		5.875%	5.875%
Preferred shares, shares outstanding (in shares) | shares		6,200,000			6,200,000		6,200,000
Liquidation Value		$ 155,000			$ 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) | shares		4,600,000			4,600,000		4,600,000
Liquidation Value		$ 115,000			$ 115,000		$ 115,000
Series H Perpetual Preferred Shares
Class of Stock [Line Items]
Preferred stock, dividend rate, percentage		6.25%			6.25%
Preferred shares, shares outstanding (in shares) | shares		4,600,000			4,600,000		0
Liquidation Value		$ 115,000			$ 115,000		$ 0
Liquidation value (in dollars per share) | $ / shares		$ 25.00			$ 25.00
Shares issued during period (in shares) | shares		4,600,000
Gross proceeds on issuance of preferred shares		$ 115,000
Stock issuance costs		$ 4,000
Class A common shares/units
Class of Stock [Line Items]
Percent of liquidation preference	50.00%
Issuance of common shares, net of offering costs (in shares) | shares	10,848,827
Stock exchange ratio	1.4275
Stock issuance costs					$ 0	$ 10,444
Common shares, par value (in dollars per share) | $ / shares		$ 0.01			$ 0.01		$ 0.01
Number of markets used in calculation of conversion ratio | market	20
Conversion ratio, maximum internal rate of return	9.00%
Redemption of participating preferred shares/units			$ 32,200