Partners' Capital, Mezzanine Capital and Distributions (Redeemable Noncontrolling Interest - Narrative) (Details)			3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 23, 2019 USD ($) d manager $ / shares	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)
Redeemable Noncontrolling Interest [Line Items]
Issuance of redeemable noncontrolling interest		$ 55,000,000
Proceeds from redeemable noncontrolling interest	$ 49,400,000
Redemption accretion of redeemable preferred noncontrolling interest	$ 151,000
Redeemable noncontrolling interest redemption value adjustments			$ (272,000)	$ 0	$ (272,000)	$ 0
Subsidiary | Alkali Holdings
Redeemable Noncontrolling Interest [Line Items]
Issuance of redeemable noncontrolling interest		$ 55,000,000
Commitment period to purchase redeemable noncontrolling interest		3 years
Facility expansion costs percentage		100.00%
Annual percentage for quarterly distributions to sponsor		10.00%
Liquidation preference per unit (in dollars per unit) | $ / shares		$ 1,000
Days after the end of fiscal quarter to pay quarterly distributions | d		45
Period following the initial closing date to pay distributions paid-in-kind		36 months
Minimum cash reserve balance required for working capital		$ 5,000,000
Preferred unit purchase price per unit (in dollars per unit) | $ / shares		$ 1,000
Period for occurrence of triggering events		6 years
Redemption accretion of redeemable preferred noncontrolling interest		$ 200,000
Redemption value of redeemable preferred noncontrolling interest		117,500,000
Redeemable noncontrolling interest redemption value adjustments					$ 300,000
Subsidiary | Alkali Holdings | Maximum
Redeemable Noncontrolling Interest [Line Items]
Redeemable noncontrolling interest preferred commitment		350,000,000
Subsidiary | Alkali Holdings | Minimum
Redeemable Noncontrolling Interest [Line Items]
Redeemable noncontrolling interest preferred commitment		$ 250,000,000
Number managers | manager		5
Number managers designated by the partnership | manager		3
Number of mangers designated by the sponsor | manager		1
Number of independent managers | manager		1