Income Taxes Tax Receivable Agreement (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Tax Receivable Agreement [Abstract]
Liabilities under tax receivable agreement		$ 52,535	$ 0
Tax Receivable Agreement, Percentage of Tax Benefits to be Paid	85.00%