Stockholders' equity (Details 2) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Outstanding	32,741,589	32,741,589
1st Qtr, 2015 [Member]
Outstanding	73,530	73,530
Weighted Average Exercise Price	7.50	7.50
2nd Qtr, 2015 [Member]
Outstanding	6,780	6,780
Weighted Average Exercise Price	8.11	8.11
3rd Qtr, 2015 [Member]
Outstanding	80,584	80,584
Weighted Average Exercise Price	3.57	3.57
4th Qtr, 2015 [Member]
Outstanding	478,312	478,312
Weighted Average Exercise Price	7.53	7.53
1st Qtr, 2016 [Member]
Outstanding	846,667	846,667
Weighted Average Exercise Price	7.16	7.16
2nd Qtr, 2016 [Member]
Outstanding	919,166	919,166
Weighted Average Exercise Price	6.28	6.28
3rd Qtr, 2016 [Member]
Outstanding	317,292	317,292
Weighted Average Exercise Price	7.13	7.13
4th Qtr, 2016 [Member]
Outstanding	355,144	355,144
Weighted Average Exercise Price	7.84	7.84
1st Qtr, 2017 [Member]
Outstanding	726,416	726,416
Weighted Average Exercise Price	6.13	6.13
2nd Qtr, 2017 [Member]
Outstanding	1,076,476	1,076,476
Weighted Average Exercise Price	7.66	7.66
3rd Qtr, 2017 [Member]
Outstanding	705,874	705,874
Weighted Average Exercise Price	6.95	6.95
4th Qtr, 2017 [Member]
Outstanding	862,339	862,339
Weighted Average Exercise Price	6.56	6.56
1st Qtr, 2019 [Member]
Outstanding	22,263,675	22,263,675
Weighted Average Exercise Price	1.09	1.09
2nd Qtr, 2019 [Member]
Outstanding	160,000	160,000
Weighted Average Exercise Price	1.15	1.15
3rd Qtr, 2019 [Member]
Outstanding	1,113,000	1,113,000
Weighted Average Exercise Price	1.16	1.16
4th Qtr, 2019 [Member]
Outstanding	2,623,000	2,623,000
Weighted Average Exercise Price	1.15	1.15
4th Qtr, 2022 [Member]
Outstanding	133,334	133,334
Weighted Average Exercise Price	7.05	7.05