Investments in WTLPG - Information for Significant Unconsolidated Equity Method Investees (Details) - WTLPG - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	12 Months Ended
	Jul. 31, 2018	Sep. 30, 2017	Dec. 31, 2016	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Total Assets	$ 928,349		$ 812,464	$ 837,163
Long-Term Debt	0		0	0
Members’ Equity/Partners' Capital	868,894		790,406	$ 787,426
Revenues	55,534	$ 87,048	88,468
Net Income	$ 16,642	$ 21,571	$ 23,883