Partners' Capital, Mezzanine Capital and Distributions (Changes in Redeemable Noncontrolling Interests) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Jul. 31, 2020	Apr. 14, 2020
Redeemable Noncontrolling Interest, Equity [Roll Forward]
Balance as of December 31, 2019		$ 125,133
Issuance of preferred units, net of issuance costs		7,457
PIK distributions		10,216
Redemption accretion		2,178
Tax distributions		(7,509)
Balance as of September 30, 2020	$ 137,475	137,475
Subsidiary | Alkali Holdings
Redeemable Noncontrolling Interest, Equity [Roll Forward]
PIK distributions	3,500	10,200
Redemption accretion	$ 700	$ 2,200
Redeemable Noncontrolling Interest [Line Items]
Equity preferred units issued (in shares)			7,609	1,750