Stock incentive plan and stock-based compensation (Details 1) (Warrant [Member], USD $)	1 Months Ended	12 Months Ended
Apr. 26, 2013	Dec. 31, 2014	Dec. 31, 2013
Warrant [Member]
Class of Warrant or Right [Line Items]
Number of warrants - Warrants outstanding		920,825	4,038,753
Number of warrants - Issued		100,000	0
Number of warrants - Exercised	(715,742)	0	(3,117,928)
Number of warrants - Expired		0	0
Number of warrants - Warrants outstanding		1,020,825	920,825
Weighted average exercise price - Warrants outstanding		$ 3.44	$ 3.68
Weighted average exercise price - Issued		$ 3.75	$ 0
Weighted average exercise price - Exercised		$ 0	$ 3.75
Weighted average exercise price - Expired		$ 0	$ 0
Weighted average exercise price - Warrants outstanding		$ 3.47	$ 3.44

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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