Other Income (Expense) - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2018
Other income (expense)
Proceeds from settlement received	$ 3.5
Minimum
Other income (expense)
Retained interest, effective interest rate (as a percent)		3.70%
Maximum
Other income (expense)
Retained interest, effective interest rate (as a percent)		12.10%
Senior Notes held by special purpose entity
Other income (expense)
Effective interest rate (as a percent)		4.90%