Summary of Significant Accounting Policies - Leases (Details) - USD ($) |
1 Months Ended | 12 Months Ended | |
|---|---|---|---|
Jul. 31, 2015 |
Dec. 31, 2018 |
Sep. 30, 2015 |
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| Lease expense | $ 3,399,000 | ||
| Lease for Offices and Research facilities in Philadelphia, U.S. | |||
| Lease term (in years) | 15 years | ||
| Early termination option (in months) | 123 months | ||
| Lease for Research and development facility in Oxfordshire, U.K. | |||
| Lease term (in years) | 25 years |
| X | ||||||||||
- Definition Represents the early termination option stated in the lease agreement. No definition available.
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| X | ||||||||||
- Definition Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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| X | ||||||||||
- Definition Amount of operating lease expense. Excludes sublease income. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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