Accrued Expenses and Other Liabilities (Details) $ in Thousands, £ in Millions	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2018 GBP (£)
Payables and Accruals [Abstract]
Compensation and benefits	$ 6,568	$ 3,296
Research and development costs	10,449	9,362
UCLB milestone	663	638	£ 0.5
Professional fees	2,611	4,130
Deferred rent		561
Corporate tax	391	620
Other liabilities	716	447
Total accrued expenses and other liabilities	21,398	19,054
Current portion of long term debt and leases	$ 300	$ 400

Accrued License Fees, Current

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Accrued Research And Development Cost, Current

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Long-term Debt, Current Maturities And Lease Incentive Liability, Current

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Carrying amount as of the balance sheet date of the unpaid sum of the known and estimated amounts payable to satisfy all currently due domestic and foreign income tax obligations.

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Carrying value as of the balance sheet date of obligations incurred and payable, pertaining to costs that are statutory in nature, are incurred on contractual obligations, or accumulate over time and for which invoices have not yet been received or will not be rendered. Examples include taxes, interest, rent and utilities. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Carrying value as of the balance sheet date of obligations incurred through that date and payable for professional fees, such as for legal and accounting services received. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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For a classified balance sheet, the cumulative difference as of the balance sheet date between the payments required by a lease agreement and the rental income or expense recognized on a straight-line basis, or other systematic and rational basis more representative of the time pattern in which use or benefit is granted or derived from the leased property, expected to be recognized in income or expense, by the lessor or lessee, respectively, within one year of the balance sheet date.

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Total of the carrying values as of the balance sheet date of obligations incurred through that date and payable for obligations related to services received from employees, such as accrued salaries and bonuses, payroll taxes and fringe benefits. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Amount of liabilities classified as other, due within one year or the normal operating cycle, if longer.

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