Selected Balance Sheet Information (Details 3) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Accrued bonus expense	$ 672	$ 1,283
Accrued severance	395	590
Accrued vacation expense	295	201
Total	$ 1,362	$ 2,074

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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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 liability, recognized in statement of financial position, for pension, other postretirement and postemployment benefits, classified as current.

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