Subsequent events (Details) (USD $)	12 Months Ended				1 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 RSU	Mar. 31, 2014 Subsequent event Options	Mar. 31, 2014 Subsequent event Executive and non executive personnel RSU
Subsequent events
Number of options for common stock granted (in shares)	1,351,000	1,391,000	2,381,000		2,030,000
Exercise price (in dollars per share)	$ 6.73	$ 8.29	$ 13.02		$ 6.1
Issued (in shares)				799,000		1,340,200