Partners' Capital, Mezzanine Capital and Distributions (Narrative) (Details) $ / shares in Units, $ in Thousands							3 Months Ended			9 Months Ended
	May 15, 2019 shares	Feb. 14, 2019 shares	Nov. 14, 2018 shares	Aug. 14, 2018 shares	May 15, 2018 shares	Sep. 01, 2017 USD ($) buyer $ / shares shares	Sep. 30, 2019 USD ($) shares	Mar. 31, 2019 $ / shares shares	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) shares	Sep. 30, 2018 USD ($)	Dec. 31, 2018 shares
Temporary Equity [Line Items]
Common units outstanding (in units)							122,579,218			122,579,218		122,579,218
Preferred units, accumulated distributions | $							$ 18,684		$ 17,635	$ 55,783	$ 51,780
Common Class A | Partners’ Capital
Temporary Equity [Line Items]
Common units outstanding (in units)							122,539,221			122,539,221
Common Class B | Partners’ Capital
Temporary Equity [Line Items]
Common units outstanding (in units)							39,997			39,997
Class A Convertible Preferred Stock Units
Temporary Equity [Line Items]
Number of convertible preferred units issued (in units)							25,336,778			25,336,778		24,438,022
Preferred units, accumulated distributions | $							$ 18,700			$ 55,800
Distributions paid-in-kind (in units)	364,180	534,576	523,132	511,934	500,976			364,180		898,756
Stock dividend rate per unit (in dollars per unit) | $ / shares								$ 0.2458
Class A Convertible Preferred Stock Units | Quarterly Rate
Temporary Equity [Line Items]
Stock dividend rate per unit (in dollars per unit) | $ / shares								0.7374
Class A Convertible Preferred Stock Units | In Arrears At Annual Rate
Temporary Equity [Line Items]
Stock dividend rate per unit (in dollars per unit) | $ / shares								$ 2.9496
Private Placement | Class A Convertible Preferred Stock Units
Temporary Equity [Line Items]
Temporary equity, stock issued during period (in shares) | $						$ 750,000
Number of convertible preferred units issued (in units)						22,249,494
Cash purchase price per unit (in dollars per unit) | $ / shares						$ 33.71
Number of initial purchasers | buyer						2