Share-based compensation (Details 2) (USD $)	6 Months Ended
Jun. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares - Exercised	715,742
Warrant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares - Warrants outstanding at December 31, 2012	4,038,753
Number of shares - Issued	0
Number of shares - Exercised	(1,022,946)
Number of shares - Expired	0
Number of shares - Warrants outstanding at June 30, 2013	3,015,807
Weighted average exercise price - Warrants outstanding at December 31, 2012	$ 3.68
Weighted average exercise price - Issued	$ 0
Weighted average exercise price - Exercised	$ 3.59
Weighted average exercise price - Expired	$ 0
Weighted average exercise price - Warrants outstanding at June 30, 2013	$ 3.71

The number of share based compensation arrangement by share based payment award warrants exercised.

No definition available.

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The number of share based compensation arrangement by share based payment award warrants expired.

No definition available.

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The number of share based compensation arrangement by share based payment award warrants issued.

No definition available.

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The number of share based compensation arrangement by share based payment award warrants outstanding.

No definition available.

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Represents share based compensation arrangement by share based payment award weighted average exercise price warrants exercised.

No definition available.

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Represents share based compensation arrangement by share based payment award weighted average exercise price warrants expired.

No definition available.

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Represents share based compensation arrangement by share based payment award weighted average exercise price warrants issued.

No definition available.

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Represents share based compensation arrangement by share based payment award weighted average exercise price warrants outstanding.

No definition available.

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