| Accounts Payable and Accrued Expenses | 12 Months Ended | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Dec. 31, 2018 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Payables And Accruals [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Accounts Payable and Accrued Expenses | 5. Accounts Payable and Accrued Expenses Accounts payable and accrued expenses consist of the following as of December 31, 2018 and 2017: 
 
 
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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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