Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Aggregate number of common shares reserved for future issuance.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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No definition available.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Gross number of share options (or share units) granted during the period.

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No definition available.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Stock options
Stock option and incentive plans
Total compensation cost	$ 1,253	$ 1,331	$ 3,079	$ 2,423
Stock Options
Outstanding (in shares)	6,618,571		6,618,571
Outstanding, weighted-average exercise price (in dollars per share)	$ 5.08		$ 5.08
Granted (in shares)	1,974,000		1,974,000
Granted (in dollars per share)	$ 3.90		$ 3.90
Stock options \| Research and development
Stock option and incentive plans
Total compensation cost	$ 611	503	$ 1,260	816
Stock options \| General and administrative
Stock option and incentive plans
Total compensation cost	642	828	1,819	1,607
Restricted stock
Stock option and incentive plans
Total compensation cost	$ 10	16	$ 20	52
Shares
Outstanding (in shares)	32,400		32,400
Issued (in shares)			0
Vested (in shares)			52,600
Restricted stock \| Minimum
Stock option and incentive plans
Vesting period			1 year
Restricted stock \| Maximum
Stock option and incentive plans
Vesting period			3 years
Restricted stock \| Research and development
Stock option and incentive plans
Total compensation cost	$ 5	5	$ 10	12
Restricted stock \| General and administrative
Stock option and incentive plans
Total compensation cost	$ 5	$ 11	$ 10	$ 40
2005 Plan
Stock option and incentive plans
Common stock reserved for issuance (in shares)	0		0
2005 Plan \| Stock options
Stock Options
Outstanding (in shares)	330,450		330,450
2014 Plan
Stock option and incentive plans
Common stock reserved for issuance (in shares)	2,018,144		2,018,144
2014 Plan \| Stock options
Stock Options
Outstanding (in shares)	5,681,121		5,681,121
Granted (in shares)	1,658,000		1,658,000
2014 Plan \| Restricted stock
Shares
Outstanding (in shares)	32,400		32,400
Equity Incentive Plan, Employee Inducments \| Stock options
Stock Options
Granted (in shares)	316,000		316,000