Fair value measurement - Non-financial assets measured at fair value on a non-recurring basis (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Assets of discontinued operations held for sale	$ 22,078	$ 135,390
Other assets	41,825	36,034
Total losses, Assets of discontinued operations held for sale	(3,166)	(65,144)	(30,900)
Total losses, Goodwill	(2,055)	(11,907)	(5,895)
Total losses, Other assets			(1,070)
Nonrecurring basis
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total losses, Assets of discontinued operations held for sale	(3,166)	(65,144)	(30,900)
Total losses, Property, plant and equipment	(2,538)	(8,153)	(6,386)
Total losses, Goodwill	(2,055)	(11,907)	(5,895)
Total losses, Other assets	(1,299)
Total losses, Other intangible assets			(1,070)
Nonrecurring basis | Fair Value
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Assets of discontinued operations held for sale	22,040	63,522	108,155
Property, plant and equipment	3,521	6,000	22,912
Goodwill	7,515	0	0
Other assets	0
Other intangible assets			1,020
Nonrecurring basis | Quoted prices in active markets for identical assets (Level 1)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Assets of discontinued operations held for sale	0	0	0
Property, plant and equipment	0	0	0
Goodwill	0	0	0
Other assets	0
Other intangible assets			0
Nonrecurring basis | Significant observable inputs (Level 2)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Assets of discontinued operations held for sale	0	0	0
Property, plant and equipment	0	0	0
Goodwill	0	0	0
Other assets	0
Other intangible assets			0
Nonrecurring basis | Significant unobservable inputs (Level 3)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Assets of discontinued operations held for sale	22,040	63,522	108,155
Property, plant and equipment	3,521	6,000	22,912
Goodwill	7,515	0	0
Other assets	0
Other intangible assets			$ 1,020