Revenue from Contracts with Customers - Performance Obligations (Details) $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Service fee and commission income recognized during the period	$ 7.9
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, expected timing of satisfaction, period	1 year
Performance obligation satisfied	40.50%