Accounts Payable and Accrued Expenses  | 
12 Months Ended | |||||||||||||||||||||||||||||||||||||||||||||
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Dec. 31, 2019  | ||||||||||||||||||||||||||||||||||||||||||||||
| Payables and Accruals [Abstract] | ||||||||||||||||||||||||||||||||||||||||||||||
| Accounts Payable and Accrued Expenses | 
 6. Accounts Payable and Accrued Expenses 
 Accounts payable and accrued expenses consisted of the following as of December 31, (in thousands): 
 
 
 Accounts payable and accrued other expenses contain unpaid general and administrative expenses and costs related to research and development that have been billed and estimated unbilled, respectively, as of year-end.  | 
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- Definition The entire disclosure for accounts payable and accrued liabilities at the end of the reporting period. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- References No definition available. 
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