Unfavorable Contracts Liability - Summary of Unfavorable Contracts Liability Activity (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2017
Unfavorable Contracts Liability [Abstract]
Balance at December 31, 2018	$ 18,885
Amortization into Wholesale revenues	(466)	$ (25,200)
Amortization into Affiliate revenue share expense	(5,834)
Balance at March 31, 2019	$ 12,585