Commitments and Contingencies - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Operating Leased Assets [Line Items]
Initial term of contract	5 years		5 years
Operating lease, rent expense	$ 1.3	$ 0.9	$ 2.4	$ 1.6
Computer and office equipment
Operating Leased Assets [Line Items]
Obligations for capital lease	$ 1.2		$ 1.2		$ 1.5
Building
Operating Leased Assets [Line Items]
Initial term of contract	12 years		12 years
Obligations for operating lease	$ 68.2		$ 68.2