Investments - Investment Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investment [Line Items]
Investment Loss (Income)	$ 17,748	$ (16,289)	$ (6,334)
White Cliffs
Investment [Line Items]
Investment Loss (Income)	(3,107)	(3,687)	(4,088)
Advantage Joint Venture
Investment [Line Items]
Investment Loss (Income)	(8,159)	(11,880)	(1,779)
Delaware Crossing
Investment [Line Items]
Investment Loss (Income)	3,061	0	0
EPIC Y-Grade
Investment [Line Items]
Investment Loss (Income)	8,381	0	0
EPIC Crude
Investment [Line Items]
Investment Loss (Income)	19,152	0	0
Other
Investment [Line Items]
Investment Loss (Income)	$ (1,580)	$ (722)	$ (467)