Shareholders' Equity / Partners' Capital - Perpetual Preferred Shares (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Sep. 30, 2017	Jun. 30, 2017
Series F Perpetual Preferred Shares
Class of Stock [Line Items]
Shares issued during period (in shares)		6,200,000
Preferred stock, dividend rate, percentage		5.875%
Proceeds from issuance of preferred stock		$ 155.0
Stock issuance costs		$ 5.3
Liquidation preference per share (in dollars per share)		$ 25.00
Series G, Preferred Perpetual Shares
Class of Stock [Line Items]
Shares issued during period (in shares)	4,600,000
Preferred stock, dividend rate, percentage	5.875%
Proceeds from issuance of preferred stock	$ 115.0
Stock issuance costs	$ 4.1
Liquidation preference per share (in dollars per share)	$ 25.00