Subsequent events (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended			3 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Mar. 31, 2013 Subsequent Event	Feb. 22, 2013 Subsequent Event Endeka	Mar. 31, 2013 Subsequent Event Restricted stock units Executive and non executive personnel
Subsequent Events:
Number of options for common stock granted (in shares)	1,391,000	2,381,000	53,000	404,800
Exercise price of option for common stock granted (in dollars per share)	$ 8.29	$ 13.02	$ 2.85	$ 6.03
Restricted stock units issued to executive and non executive personnel						602,058
Amount of all outstanding stock of acquired entity					$ 5,300