Partners' Capital, Equity and Incentive Compensation Plans - Schedule of Quarterly Cash Dividends (Details) - USD ($) $ / shares in Units, $ in Millions											6 Months Ended
	Jul. 15, 2021	Jul. 07, 2021	Apr. 15, 2021	Apr. 06, 2021	Jan. 15, 2021	Jan. 07, 2021	Apr. 15, 2020	Apr. 07, 2020	Jan. 15, 2020	Jan. 07, 2020	Jun. 30, 2021	Jun. 30, 2020
Series A Preferred Stock
Per Share and Per Unit Rate (in dollars per share)			$ 0.45		$ 0.45		$ 0.45		$ 0.45
Aggregate Dividend/Distribution Amount			$ 1.9		$ 1.9		$ 1.9		$ 1.9		$ 3.8	$ 3.8
Series A Preferred Stock | Subsequent Event
Per Share and Per Unit Rate (in dollars per share)	$ 0.45
Series B Preferred Stock
Per Share and Per Unit Rate (in dollars per share)			$ 1.63		$ 1.63		$ 1.63		$ 1.63
Aggregate Dividend/Distribution Amount			$ 5.1		$ 5.1		$ 5.1		$ 5.1		10.2	10.2
Series B Preferred Stock | Subsequent Event
Per Share and Per Unit Rate (in dollars per share)	$ 1.63
Common stock
Per Share and Per Unit Rate (in dollars per share)				$ 0.50		$ 0.47		$ 0.47		$ 0.44
Aggregate Dividend/Distribution Amount				$ 35.7		$ 33.4		$ 31.5		$ 28.6	$ 69.1	$ 60.1
Common stock | Subsequent Event
Per Share and Per Unit Rate (in dollars per share)		$ 0.50