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Capital Structure - Summary of Ordinary Shares (Details)	3 Months Ended
	Mar. 31, 2019 shares
Ordinary Shares [Roll Forward]
Ordinary shares in issue as at December 31, 2018	59,743,156
Ordinary shares issued to employees under the 2013 share incentive plan and/or 2008 share purchase plan	144,269
Ordinary shares issued to non-employee directors	6,993
Ordinary shares canceled	59,894,418
Total ordinary shares of 0.015144558c per share in issue	0
Ordinary shares in issue as at March 31, 2019	60,395,839

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Ordinary Shares [Roll Forward]

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Previous Common Stock, Shares Issued

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Stock issued during period shares non employee options.

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- Definition

Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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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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Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

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