Shareholders' Equity / Partners' Capital - At the Market Common Share Offering Program (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2017	Sep. 30, 2016	Aug. 31, 2017	Nov. 30, 2016
Class of Stock [Line Items]
Proceeds from issuance of shares/units			$ 694,765,000	$ 0
Class A common shares/units
Class of Stock [Line Items]
Shares issued during period (in shares)	13,800,000	14,842,982
Proceeds from issuance of shares/units		$ 336,500,000
Stock issuance costs	$ 9,200,000	$ 300,000	$ 10,444,000	$ 0
At the Market - Common Share Offering Program | Class A common shares/units
Class of Stock [Line Items]
Shares authorized for future issuance, value					$ 500,000,000	$ 400,000,000
Shares issued during period (in shares)			2,000,000
Proceeds from issuance of shares/units			$ 46,200,000
Shares issued, price per share (in dollars per share)	$ 22.74		$ 22.74
Proceeds from issuance of common stock, net of issuance costs			$ 45,600,000
Stock issuance costs			600,000
Shares available for future issuance, value	$ 500,000,000		$ 500,000,000