Share-based compensation (Details 2) (USD $)	9 Months Ended
Sep. 30, 2013
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	(2,504,432)
Number of shares - Expired	0
Number of shares - Warrants outstanding at September 30, 2013	1,534,321
Weighted average exercise price - Warrants outstanding at December 31, 2012	$ 3.68
Weighted average exercise price - Issued	$ 0
Weighted average exercise price - Exercised	$ 3.73
Weighted average exercise price - Expired	$ 0
Weighted average exercise price - Warrants outstanding at September 30, 2013	$ 3.60
Warrant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares - Exercised	715,742

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.

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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.

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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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