Stock incentive plan and share-based compensation (Details)		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2012 All Option Plans [Member] USD ($)	Jun. 30, 2012 All Option Plans [Member] GBP (£)
Number of Shares,Outstanding at December 31, 2011	6	11	11
Number of Shares,Granted		0	0
Number of Shares,Exercised		0	0
Number of Shares,Forfeited/ Cancelled		(5)	(5)
Number of Shares,Outstanding at June 30, 2012	6	6	6
Weighted-Average Exercise Price,Outstanding at December 31, 2011		$ 58,500	£ 35,700
Weighted-Average Exercise Price,Forfeited/ Cancelled		$ 30,917	£ 19,500
Weighted-Average Exercise Price,Outstanding at June 30, 2012		$ 46,326	£ 29,250
Number of shares Exercisable at December 31, 2011		10	10
Number of shares Exercisable at June 30, 2012		6	6
Weighted-Average Exercise Price, Exercisable at December 31, 2011		$ 58,500	£ 35,700
Weighted-Average Exercise Price, Exercisable at June 30, 2012		$ 46,326	£ 29,250