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Composition of Certain Financial Statement Captions - Accounts Payable and Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts Payable and Accrued Expenses [Abstract]
Accrued expenses		$ 824	$ 1,182
Accounts payable		721	1,297
Accrued payroll and bonus		423	750
Accrued legal fees		186	509
Accrued vacation		192	64
Accrued R&D studies		230	285
Other current liabilities		201	119
Accounts payable and accrued expenses, Total	$ 2,729	$ 2,777	$ 4,206

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- Definition

Carrying value as of the balance sheet date of obligations incurred through that date and payable for professional fees, such as for legal services received.

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Carrying value as of the balance sheet date of obligations incurred through that date and payable for research and development studies.

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Sum of the carrying values as of the balance sheet date of obligations incurred through that date and due within one year (or the operating cycle, if longer), including liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received, taxes, interest, rent and utilities, accrued salaries and bonuses, payroll taxes and fringe benefits.

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-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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Carrying value as of the balance sheet date of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. 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 and payable for incentive compensation awarded to employees and directors or earned by them based on the terms of one or more relevant arrangements. 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 and payable for unused vacation time owed to employees based on the entity's vacation benefit given to its employees. 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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