Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Defined benefit pension plan, tax benefits	$ 900		$ 900
Total Members’ Capital
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unamortized defined benefit pension plan net actuarial losses	3,300		3,400
AOCI Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss included in noncontrolling interest	2,000		$ 2,100
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassifications from accumulated other comprehensive loss	$ 67	$ 46