Partners' Capital, Equity and Incentive Compensation Plans (Summary of Equity Issued) (Details) - USD ($) shares in Thousands, $ in Thousands	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Subsidiary, Sale of Stock [Line Items]
Forward Shares Sold	10,299	5,781	3,795
Remaining Expected Proceeds Available	$ 590,557	$ 304,448	$ 177,845
February 2019 Offering
Subsidiary, Sale of Stock [Line Items]
Forward Shares Sold		(931)
Remaining Expected Proceeds Available		$ (35,841)
June 2019 Prior ATM Program - Sales
Subsidiary, Sale of Stock [Line Items]
Forward Shares Sold	634	3,917
Remaining Expected Proceeds Available	$ 33,643	$ 209,934
June 2019 Prior ATM Program - Settlements
Subsidiary, Sale of Stock [Line Items]
Forward Shares Sold	(1,033)	(1,000)
Remaining Expected Proceeds Available	$ (51,162)	$ (47,490)
May 2020 ATM Program - Sales
Subsidiary, Sale of Stock [Line Items]
Forward Shares Sold	517
Remaining Expected Proceeds Available	$ 31,690
June 2020 Offering - Sales
Subsidiary, Sale of Stock [Line Items]
Forward Shares Sold	4,400
Remaining Expected Proceeds Available	$ 271,938