Property, plant and equipment (Capital Leases) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Assets under capital leases
Assets under capital leases, gross	$ 5,563	$ 5,391
Less: Accumulated depreciation	(1,317)	(1,164)
Assets under capital leases, net	4,246	4,227
Freehold and leased land and buildings
Assets under capital leases
Assets under capital leases, gross	4,548	4,461
Machinery and equipment
Assets under capital leases
Assets under capital leases, gross	914	828
Fixtures, fittings and office equipment
Assets under capital leases
Assets under capital leases, gross	$ 101	$ 102