Share-based compensation - Summary of Status of Company's Stock Option Plan (Details) - $ / shares	6 Months Ended	12 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Shares
Outstanding at beginning of period	4,415,397	3,069,440	3,069,440
-Exercised	(10,000)		(5,000)
-Granted	284,800	231,500	3,874,200
-Cancelled			(2,523,243)
Outstanding at end of period	4,690,197		4,415,397
Weighted Average Exercise Price
Outstanding at beginning of period	$ 1.20	$ 4.28	$ 4.28
-Exercised	0.89		3.43
-Granted	1.29		1.19
-Cancelled			4.92
Outstanding at end of period	$ 1.20		$ 1.20

No definition available.

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- Definition

The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

+ References

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- Definition

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

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- Definition

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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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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- Definition

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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- Definition

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

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- Definition

Weighted average price at which option holders acquired shares when converting their stock options into shares.

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- Definition

Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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- Definition

Number of share options (or share units) exercised during the current period.

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