Income Taxes (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Income Taxes
Interest held by parent	62.80%			61.50%
Interest held by non-controlling owners	37.20%			38.50%
Income tax (expense) benefit	$ 1,067,000	$ 0
Effective tax rate	21.20%	0.00%
Anticipated Tax Distributions	$ 434,000
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			21.00%	35.00%