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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- Definition

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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No definition available.

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Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Stock options
Stock option and incentive plans
Total compensation cost	$ 1,331	$ 664	$ 2,423	$ 1,325
Stock Options
Outstanding (in shares)	4,741,109		4,741,109
Outstanding, weighted-average exercise price (in dollars per share)	$ 5.50		$ 5.50
Granted (in shares)			1,121,000
Granted (in dollars per share)			$ 6.36
Stock options \| Research and development
Stock option and incentive plans
Total compensation cost	$ 503	175	$ 816	370
Stock options \| General and administrative
Stock option and incentive plans
Total compensation cost	828	489	1,607	955
Restricted stock
Stock option and incentive plans
Total compensation cost	$ 16	108	$ 52	$ 194
Shares
Outstanding (in shares)	117,867		117,867
Issued (in shares)			0	245,200
Vested (in shares)			113,933
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	31	$ 12	$ 49
Restricted stock \| General and administrative
Stock option and incentive plans
Total compensation cost	$ 11	$ 77	$ 40	$ 145
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)	362,112		362,112
2014 Plan
Stock option and incentive plans
Common stock reserved for issuance (in shares)	1,286,003		1,286,003
2014 Plan \| Stock options
Stock Options
Outstanding (in shares)	4,378,997		4,378,997
2014 Plan \| Restricted stock
Shares
Outstanding (in shares)	117,867		117,867