Represents the increase in number of shares available for grant during the period.

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The number of vested and unvested awards modified under an equity-based compensation plan.

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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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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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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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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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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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An excess of the fair value of the modified award over the fair value of the award immediately before the modification.

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Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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Number of shares (or other type of equity) issued during the period as a result of any equity-based compensation plan other than an employee stock ownership plan (ESOP), net of any shares forfeited. Shares issued could result from the issuance of restricted stock, the exercise of stock options, stock issued under employee stock purchase plans, and/or other employee benefit plans.

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Stock-Based Compensation - Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended		6 Months Ended
	Feb. 28, 2018	Jan. 31, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Share-based Compensation
Shares available for future issuance (in shares)			826,988		826,988		83,929
Number of stock options granted (in shares)					310,715
Options remained outstanding			1,696,187		1,696,187		1,593,195
Total grant date fair value of options vested			$ 545,000	$ 797,000	$ 922,000	$ 904,000
Unrecognized compensation expense, weighted-average period expected to be recognized					2 years 10 months 24 days
Weighted-average exercise price (per share)	$ 7.64	$ 16.25	$ 7.28		$ 7.28		$ 8.88
Stock-based compensation expense			$ 717,000	$ 408,000	$ 1,342,000	$ 839,000
Immediate vesting
Share-based Compensation
Incremental modification value	$ 63,000
Remaining vesting
Share-based Compensation
Incremental modification value	$ 537,000
Chief Executive Officer
Share-based Compensation
Number of vested and unvested stock option award modified	400,000
Incremental modification value	$ 600,000
Employees
Share-based Compensation
Weighted-average grant date fair value of options granted			$ 4.14	$ 5.25	$ 4.56	$ 4.67
Stock-based compensation expense			$ 688,000,000	$ 319,000,000	$ 1,300,000	$ 740,000
Non-Employee
Share-based Compensation
Number of stock options granted (in shares)			0	0	7,200	0
Options remained outstanding			45,072		45,072
Weighted-average exercise price (per share)			$ 9.15		$ 9.15
Stock-based compensation expense			$ 29,000	$ 89,000	$ 44,000	$ 99,000
2016 Employee Stock Purchase Plan
Share-based Compensation
Increase in number of shares available for grant		128,172
Shares available for future issuance (in shares)			291,659		291,659
Number of shares issued (in shares)			20,057	17,924	20,057	17,924
Value of share issued			$ 137,000		$ 137,000	$ 122,000