Subsequent events (Details) (Common stock, USD $)	12 Months Ended		0 Months Ended
Subsequent events (Details) (Common stock, USD $)	Dec. 31, 2014	Dec. 31, 2013	Jan. 28, 2015
Subsequent Event [Line Items]
Shares of common stock issued in private placements	647,706
Private placements, price in usd per share	$ 4.75
Private Placement
Subsequent Event [Line Items]
Shares of common stock issued in private placements	1,400	1,476,789
Private Placement \| Subsequent event
Subsequent Event [Line Items]
Shares of common stock issued in private placements			210,526
Private placements, price in usd per share			$ 4.75
Proceeds from stock issuance			$ 1,000,000