Revenue - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue from Contract with Customer [Abstract]
Revenue from expense reimbursement	$ 1.3	$ 2.7	$ 2.3	$ 5.0