Investments Equity Method Investments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Equity Method Investments and Joint Ventures [Abstract]
Variable Interest Entity, Qualitative or Quantitative Information, Date Involvement Began			Sep. 25, 2017
Variable Interest Entity, Financial or Other Support, Amount			$ 200,000
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage			66.70%
Variable Interest Entity, Measure of Activity, Other, Amount			$ 34,600
Variable Interest Entity, Measure of Activity, Purchases			21,700
Income (Loss) from Equity Method Investments	$ 2,971	$ 0	2,971	$ 0
Equity Method Investments	17,748		17,748		$ 0
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	$ 17,748		$ 17,748