Commitments and Contingencies - Licensor Expense Reimbursement (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Licensor Expense Reimbursement
Commitments and contingencies
Expense for prosecution and maintenance of patent rights	$ 18.2	$ 23.1	$ 9.4

Professional and contract service expense includes cost reimbursements for support services related to contracted projects, outsourced management, technical and staff support.

No definition available.

Name:	us-gaap_ProfessionalAndContractServicesExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration