Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

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Commitments and Contingencies - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Operating Leased Assets [Line Items]
Initial term of contract	5 years		5 years
Operating lease, rent expense	$ 1.4	$ 1.0	$ 3.8	$ 2.6
Computer and office equipment
Operating Leased Assets [Line Items]
Obligations for capital lease	$ 1.1		$ 1.1		$ 1.5
Building
Operating Leased Assets [Line Items]
Initial term of contract	12 years		12 years
Obligations for operating lease	$ 68.2		$ 68.2