Revenue Recognition Revenue Remaining Performance Obligation, Expected Timing of Satisfaction (Details) $ in Millions	Dec. 31, 2018 USD ($)
Revenue Recognition [Abstract]
Revenue expected to be recognized on VCP contracts sold as of period end	$ 92.9
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue Recognition [Abstract]
Revenue expected to be recognized on VCP contracts sold as of period end	$ 31.0
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue Recognition [Abstract]
Revenue expected to be recognized on VCP contracts sold as of period end	$ 46.4
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	2 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue Recognition [Abstract]
Revenue expected to be recognized on VCP contracts sold as of period end	$ 15.5
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	2 years